Gerald L. Stapleton and Luke R. Ray appeal decisions by the Benefits Review Board (BRB) denying black lung benefits. Mullins Coal Company appeals a decision of the BRB granting black lung benefits to Glenn Cornett. These cases each involved the interim presumption and its rebuttal under 20 C.F.R. § 727.203 and were consolidated for the purpose of appeal.
For the reasons variously expressed in the opinions of Judges Hall, Sprouse, and Widener (which opinions, one or others, are joined by Chief Judge Winter and Judges Chapman, Wilkinson and Sneeden), we hold that the interim presumption under § 727.203(a)(1), (2), or (3) is established when there is credible evidence that a qualifying X-ray indicates the presence of pneumoconiosis, a single qualifying set of ventilatory studies indicates, pursuant to the regulatory standard, a chronic respiratory or pulmonary disease, or a single qualifying set of blood gas studies indicates, pursuant to the regulatory standard, an impairment in the transfer of oxygen from the lungs to the blood.
For the reasons variously expressed in the opinions of Judges Hall, Sprouse, and Widener (which opinions, one or others, are joined by Chief Judge Winter and Judges Chapman, Wilkinson and Sneeden), we hold that the interim presumption under § (a)(4) is established by one qualifying physician’s opinion, i.e., one which meets the regulations’ requirements.
For reasons variously expressed in the opinions of Judges Phillips and Widener (which opinions, one or the other, are joined by Judges Russell, Murnaghan, Ervin, Chapman, and Wilkinson), we hold that, absent a qualifying physician's opinion, the interim presumption under (a)(4) is established by weighing, under the custom*427ary rules of evidence (which require the facts upon which a presumption is based to be proven by a preponderance of the evidence), the “other medical evidence,” i.e., medical evidence other than X-rays, ventilatory studies, and blood gas studies.
For the reasons variously expressed in the opinions of Judges Phillips and Widener (which opinions, one or the other, are joined by Judges Russell, Murnaghan, Ervin, Chapman, and Wilkinson), we hold that, when considering under 20 C.F.R. § 727.203(b) the rebuttal of a presumption established under § (a), all relevant medical evidence must be considered and weighed, including, but not exclusively, nonqualifying X-rays, test results, and opinions, regardless of the section under which the presumption was invoked. This consideration is limited only by the single X-ray statute, 30 U.S.C. § 923(b) (a claim may not be denied solely on the basis of one negative chest X-ray).
For the reasons variously expressed in the opinions of Judges Hall, Sprouse, and Widener (which opinions, one or others, are joined by Chief Judge Winter and Judges Chapman, Wilkinson and Sneeden), Consolidated Coal Company v. Sanati, 713 F.2d 480 (4th Cir.1983), is overruled insofar as it holds that one qualifying physician’s opinion does not necessarily invoke the presumption, but, for the reasons expressed in the opinions of Judges Phillips and Widener (which opinions, one or the other, are joined by Judges Russell, Murnaghan, Ervin, Chapman, and Wilkinson), its reasoning remains the law in this circuit in considering whether or not the presumption is established under (a)(4) in the absence of a qualifying physician’s opinion.
For the reasons variously expressed in the opinions of Judges Phillips and Widener (which opinions, one or the other, are joined by Judges Russell, Murnaghan, Ervin, Chapman, and Wilkinson), we hold that Whicker v. United States Department of Labor Benefits Review Board, 733 F.2d 346 (4th Cir.1984), and Hampton v. United States Department of Labor Benefits Review Board, 678 F.2d 506 (4th. Cir.1982) (per curiam), are overruled.
For the reasons expressed in part IIIB of Judge Hall’s opinion (which is joined by all of the judges), we hold that interest on an award of black lung benefits shall accrue only from thirty days after the first agency decision awarding benefits.
Accordingly, our decision in each of the three consolidated cases is as follows:
Gerald L. Stapleton: The ALJ properly invoked the interim presumption and correctly found it rebutted. Staple-ton’s claim for benefits was properly denied. We affirm.
Luke R. Ray: The ALJ should have invoked the interim presumption. The BRB’s decision is vacated, and Ray’s claim is remanded for a determination of whether or not the presumption is rebutted.
Mullins Coal Company: The ALJ properly invoked the interim presumption and found it unrebutted. We affirm the award of benefits to Glenn Cor-nett. We remand, however, for a calculation of interest on his benefits in accordance with this opinion.
K.K. HALL, Circuit Judge:
I.
Introduction
These three black lung cases were consolidated for en banc review, because they each involve a common legal issue, concerning the type and quantum of proof necessary to trigger and rebut the interim presumption of pneumoconiosis under 20 C.F.R. § 727.203, and because our past panel decisions in this area have been contradictory and confusing.1 The regulation at issue states in pertinent part as follows:
*428§ 727.203 Interim presumption
(a) Establishing interim presumption.
A miner who engaged in coal mine employment for at least 10 years will be presumed to be totally disabled due to pneumoconiosis, or to have been totally disabled due to pneumoconiosis at the time of death, or death will be presumed to be due to pneumoconiosis, arising out of that employment, if one of the following medical requirements is met:
(1) A chest roentgenogram (X-ray), biopsy, or autopsy establishes the existence of pneumoconiosis ...;
(2) Ventilatory studies establish the presence of a chronic respiratory or pulmonary disease (which meets the requirements for duration in § 410.412(a)(2) of this title) as demonstrated by values which are equal to or less than [certain values specified in the regulation’s tables];
(3) Blood gas studies which demonstrate the presence of an impairment in the transfer of oxygen from the lung alveoli to the blood as indicated by values which are equal to or less than [certain values specified in the regulation’s tables];
(4) Other medical evidence, including the documented opinion of a physician exercising reasoned medical judgment, establishes the presence of a totally disabling respiratory or pulmonary impairment; ...
(b) Rebuttal of interim presumption.
In adjudicating a claim under this sub-part, all relevant medical evidence shall be considered. The presumption in paragraph (a) of this section shall be rebutted if:
(1) The evidence establishes that the individual is, in fact, doing his usual coal mine work or comparable and gainful work ...; or
(2) In light of all relevant evidence it is established that the individual is able to do his usual coal mine work or comparable and gainful work .. or
(3) The evidence establishes that the total disability or death of the miner did not arise in whole or in part out of coal mine employment; or
(4) The evidence establishes that the miner does not, or did not, have pneumoconiosis.
II.
Factual Background
A. Stapleton
Stapleton was forty-three years old in 1980 when his claim for black lung benefits was heard by an Administrative Law Judge (“ALJ”). Stapleton had worked in coal mines for at least fifteen to sixteen years and was last employed by respondent, Westmoreland Coal Company (“Westmoreland”), from May, 1969, until June, 1972. At that time, he stopped working as a result of breathing difficulties and heart problems.
A 1973 x-ray noted minimal pneumonitis but otherwise clear lungs. An x-ray read by Dr. Shiv Navani, a B reader,2 on November 30, 1976, indicated an increase in small nodular and linear densities throughout the lungs consistent with changes of coal worker’s pneumoconiosis. Another x-ray dated January 21, 1980, was read by Dr. John G. Byers, a B reader, who concluded there was “essentially” no evidence of pneumoconiosis. This x-ray was re-read by Dr. Paul Francke, also a B reader, on July 24, 1980. Dr. Francke found no x-ray evidence of pneumoconiosis.
There were two pulmonary function studies received into the record. A 1976 study showed qualifying values, i.e. values below the maximum values specified in the regulation, but noted poor effort on the part of Stapleton. A 1980 study reflected non-qualifying values, i.e. values above the maximum, and likewise indicated poor effort and cooperation.
Also introduced into the record were two arterial blood gas studies, one performed in *4291976 and another conducted in 1980. The results of both studies were above the regulation’s maximum values and were, therefore, non-qualifying.
In addition, the evidence included medical reports of various physicians. In a report dated March, 1973, Anthony F. Leger, M.D., one of Stapleton’s treating physicians, stated that claimant suffers from sinus tachycardia (rapid heart beat) and was hospitalized in July, 1972, because of his heart disorder. Dr. Leger also noted that Stapleton had been hospitalized in Norton, Virginia, in December, 1970, when he developed acute back pain while lifting a heavy object. There is no reference in Dr. Leger’s records to any pulmonary or respiratory difficulty.
In a letter dated June 23, 1973, Daniel Gabriel, M.D., Stapleton’s regular treating physician, wrote to claimant’s counsel as follows:
I wish I could give you a more favorable report.
I first saw Mr. Stapleton in June, 1972 with chief complaint of shortness of breath, chest pain and rapid heart. At my insistence, he quit working because of his heart condition.
In my letter to you of 1972 concerning his low back injury in 1970, it did not disable him for work as you know he was working. I have no records of this condition other than his statement.
Dr. S.K. Paranthaman, who examined the claimant in 1976 at the request of the United States Department of Labor, found that Stapleton had evidence of pneumoconiosis and possible bronchitis. Dr. Paranthaman noted, however, that claimant’s respiratory impairment was moderate and that “the functional impairment appears to be primarily from cardiac condition and back pain.”
Stapleton was also examined in April, 1980, by Dr. John G. Byers, who concluded that there was not sufficient evidence to justify a diagnosis of pneumoconiosis. According to Dr. Byers, claimant had “no significant pure respiratory symptoms other than dyspnea,” which the physician attributed to Stapleton’s cardiac disease. Dr. Byers further stated that:
Disability is difficult to evaluate in this gentleman’s case. His respiratory impairment is not fully evaluated because of his poor co-operation on pulmonary function testing. Certainly the best curve that he was able to give us would not indicate significant respiratory impairment. There is an abnormality of arterial blood gases which is not fully explained and which might be associated with dyspnea on moderate exertion. I am attributing this abnormality to temporary factors associated with his heart rate of 160 beats per minute caused by his cardiac disease. Note that several years ago PO¿ was in the normal range on another test. I think this patient has significant disability based on neurosis, and he probably has significant disability based on his cardiac disease which is not yet in control on his Inderal____ As noted above, I feel that this patient’s primary impairment is cardiac in nature with a strong component of cardiac neurosis.
A report, dated June 30, 1980, was submitted by Dr. George O. Kress, a specialist in industrial pulmonary medicine. Dr. Kress, a non-examining physician, reviewed the record and concluded that Stapleton did not suffer from pneumoconiosis, or from any significant respiratory problems. According to Dr. Kress, problems unrelated to claimant’s coal mine employment probably precluded his ability to do work requiring significant effort.
Based on this evidence, the ALJ invoked the interim presumption under 20 C.F.R. § 727.203(a)(1), citing Dr. Navani’s positive x-ray, but concluded that the presumption was adequately rebutted by other medical evidence under 20 C.F.R. § 727.203(b)(4), which included the more recent negative x-ray report of Dr. Byers. The ALJ also concluded that no other evidence qualified Stapleton as disabled due to a respiratory or pulmonary impairment. The one set of positive ventilatory studies was discounted because of poor cooperation. The ALJ, *430therefore, denied benefits. In reviewing this decision, the Board concluded that, although the ultimate decision denying benefits was correct, the AU had improperly invoked the presumption on the basis of the one positive x-ray.
B. Ray
Ray is a forty-seven year-old former coal miner who had sixteen years of coal mining employment when he quit working in 1973 due to stomach problems. Ten x-rays, six ventilatory studies, and six medical reports were introduced at the hearing on his claim for black lung benefits.
Among the x-ray reports was one in 1974 which was positive for pneumoconiosis but which was submitted by an unidentified reader with an illegible signature. A 1977 x-ray was interpreted as positive by one radiologist. The most recent x-ray in 1980 showed a “suspicion” of pneumoconiosis. All of the remaining x-rays were negative.
Two of the six doctors’ reports showed pulmonary disability, but these were not given great weight by the AU because they failed to conclude definitively that the disability was from exposure to coal dust. One doctor reported in 1975 that it was “probably” due to coal dust. Another physician concluded in 1980 that it was due to cigarette smoking. A third doctor found Ray totally disabled in 1977; however, the blood gas and ventilatory studies performed by this physician were normal. Ray’s treating physician diagnosed anxiety neurosis and chronic gastritis and stated in a letter dated July, 1979, “[a]s far as his pulmonary complaints are concerned, I think they are rather insignificant.”
There were two positive ventilatory studies. The AU, however, found them to be outweighed by more recent negative studies. The AU, concluding that the presumption had not been triggered, denied benefits, and the Board affirmed.
C. Mullins
Cornett, who was employed in coal mines for approximately thirty-six years, worked for Mullins from June, 1967, to April 30, 1976. In 1977, claimant suffered a heart attack. At that time his family physician, L.J. Fleenor, M.D., informed him he was suffering from black lung disease. Claimant tried to return to his coal mine employment, but suffered from shortness of breath and coughing. In less than a year, he completely ceased work at the coal mine and began to work at his family’s hardware store.
The medical evidence, introduced in connection with Cornett’s claim for black lung benefits, included both positive and negative x-rays, as well as qualifying and non-qualifying ventilatory and blood gas studies. In addition, there were conflicting opinions of two physicians. Dr. Fleenor submitted a report, dated February, 1979, in which he diagnosed black lung disease. Robert A. Abernathy, M.D., a specialist in internal medicine, examined Cornett in January, 1980, and concluded that his “major problem appears to be related chiefly to his hypertension and to his heart disease.” Dr. Abernathy recognized that Cornett “does appear to have some pulmonary impairment” and was precluded from returning to coal mining work; however, in a supplemental report dated August 1, 1980, Dr. Abernathy expressed his belief that claimant’s breathing problems were related not to his exposure to coal dust but to his hypertension, cardiovascular impairments, and possibly smoking.
Following the administrative hearing on Cornett’s claim, the AU found that claimant was entitled to invoke the presumption under 20 C.F.R. § 727.203(a)(1), (a)(2), and (a)(3). As for rebuttal, the AU concluded that:
the medical evidence consisting of Claimant’s ventilatory studies, blood-gas tests, and Dr. Abernathy’s opinion that the Claimant is substantially precluded from doing any work beyond what he appears to be doing at the hardware store overwhelming [sic] establishes a respiratory impairment that causes Claimant to be incapable of performing his usual or comparable work____
*431Dr. Fleenor also diagnosed cardiovascular disease in addition to category 1 pneumoconiosis and he attributed Claimant’s disability to both impairments. Testimonial evidence has established that Dr. Fleenor is Claimant’s treating physician. Further, there is no indication that Dr. Abernathy has examined the Claimant more than once. Therefore, Dr. Flee-nor’s opinion may be given greater weight than that of a physician who has examined the Claimant on only one occasion.
The ALJ awarded benefits, and also awarded interest at a rate of six percent per year to commence as of July, 1978, the date of claimant’s eligibility. The Board affirmed.3
III.
Discussion
In our order setting these three appeals for en banc argument, the parties were requested to address the following issues:
(1) Whether, despite the evidence of negative or non-qualifying x-rays, ventilatory studies, blood gas studies, and/or physicians’ opinions, the interim presumption of pneumoconiosis under 20 C.F.R. § 727.203(a) is automatically triggered by any one of the following:
(a) one positive x-ray;
(b) one set of positive ventilatory studies;
(c) one set of positive blood gas studies;
(d) one physician’s opinion.
(2) Once the interim presumption of pneumoconiosis is triggered, whether and to what extent is non-qualifying medical evidence permitted to rebut the presumption under 20 C.F.R. § 727.-203(b).
In addition to these common issues, the Court must consider in Mullins whether it is proper in black lung cases to award interest to a claimant on past due benefits from the date he is eligible for payment rather than from the time a favorable decision is issued.
In Section III.A. of this opinion, I will address first the issues concerning the interim presumption. I am authorized to state that Chief Judge Winter, Judge Sprouse, and Judge Sneeden join me in Section III.A. Section III.B. sets forth the Court’s unanimous opinion concerning the pre-judgment interest issue raised in Mullins.
A. Interim Presumption
Black lung disease, or pneumoconiosis, is a severe and frequently crippling chronic respiratory impairment which is caused by long-term inhalation of coal mine dust. See Usery v. Turner Elkhorn Mining Co., 428 U.S. 1, 6-7, 96 S.Ct. 2882, 2888, 49 L.Ed.2d 752 (1976). The federal black lung program was enacted to provide benefits for total disability due to black lung disease. The program was originally enacted in Title IV of the Federal Coal Mine Health and Safety Act of 1969, Pub.L. No. 91-173, 83 Stat. 792 (1969). The program has been amended on three occasions: Black Lung Benefits Amendments of 1972, Pub.L. No. 92-303, 86 Stat. 150 (1972) (the “1972 amendments”); Black Lung Benefits Revenue Act of 1977, Pub.L. No. 95-227, 92 Stat. 11 (1977) and Black Lung Benefits Reform Act of 1977, Pub.L. No. 95-239, 92 Stat. 95 (1977), signed into law on March 1, 1978 (the “1978 amendments”); and Black Lung Benefits Amendments of 1981, Pub.L. No. 97-119, 95 Stat. 1643 (1981) (the “1981 amendments”).
The responsibility for adjudicating claims has shifted from the Social Security Administration (the “SSA”) to the Department of Labor (the “DOL”). The 1972 amendments provided that claims filed on or before June 30, 1973 (Part “B” claims) would be adjudicated by SSA. See generally 20 C.F.R. Part 410. Claims filed after that date (Part *432“C” claims) would be adjudicated by DOL. Under this system, Part “C” claimants were subjected to more restrictive eligibility criteria than Part “B” claimants. The 1978 amendments, however, eliminated the restrictive standards applicable to Part “C” claims, liberalized the statutory eligibility criteria, and authorized the Secretary of Labor to adopt new criteria which were no more restrictive than the eligibility standards governing Part “B” claims. 30 U.S.C. § 902(f)(2). In accordance with this intent and pursuant to 30 U.S.C. § 902(f),4 the Secretary promulgated interim criteria at 20 C.F.R. § 727.200 et seq., including the presumption at issue in these appeals at § 727.203,5 which is set out in full in the Introduction to this opinion.
The employers in each case, as well as the Director of the Office of Workers’ Compensation Programs (“Director”), whom we permitted to intervene in these appeals, contend that the regulation at 20 C.F.R. § 727.203(a) requires the ALJ to weigh all evidence, both positive and negative, before invoking the interim presumption. Under this view, the presumption is triggered only if there is a preponderance of like-kind positive evidence. According to the employers and the Director, the presumption is not triggered by a single positive x-ray, ventilatory or blood gas test, or by one physician’s opinion, unless that single piece of evidence stands uncontradicted by like-kind evidence. I cannot agree. Although, as the opinion of Judge Phillips indicates, the Director’s view on this issue is, if reasonable, entitled to judicial deference, I find that the agency’s interpretation renders the regulation internally inconsistent and is plainly erroneous. Moreover, I conclude that the agency’s interpretation-conflicts with congressional intent.
Legal presumptions, such as the one at issue in these appeals, are encountered in a variety of civil, criminal and administrative settings. A presumption is raised by a basic fact or facts which, when accepted as true by the factfinder, give rise to a mandatory inference called a presumed fact. Graham C. Lilly, An Introduction to the *433Law of Evidence, Chapter III, at 49 (1978). “Once the basic [fact or] facts are believed, the resulting presumed fact must be accepted by the trier unless it is rebutted by contravening evidence.” Id.
The initial burden of meeting the factual prerequisite for triggering a presumption is distinct from the ultimate burden of convincing the factfinder of the existence of all the essential elements of a claim or defense. Meeting the initial burden, however, has the effect of shifting the burden of persuasion, or at least the burden of coming forward with rebuttal evidence, onto the opposing party. Id. at 49, 54-58.
With these principles in mind, I have examined the statutory and regulatory scheme of the presumption at issue in these appeals. At the outset I note that Congress has mandated that in deciding black lung claims all relevant evidence be considered:
In determining the validity of claims under this part, all relevant evidence shall be considered, including, where relevant, medical tests such as blood gas studies, X-ray examination, electrocardiogram, pulmonary function studies, or physical performance tests, and any medical history, evidence submitted by the claimant’s physician, or his wife’s affidavits, and in the case of a deceased miner, other appropriate affidavits of persons with knowledge of the miner’s physical condition, and other supportive materials.
30 U.S.C. § 923(b).
The Conference Report, accompanying the 1978 amendments, states that:
With respect to a claim filed or pending prior to the promulgation of such [new] regulations such regulations shall not provide more restrictive criteria than those applicable to a claim filed on June 30, 1973, except that in determining claims under such criteria all relevant medical evidence shall be considered in accordance with standards prescribed by the Secretary of Labor and published in the Federal Register.
H.R.Rep. No. 864, 95th Cong., 2d Sess., reprinted in [1978] U.S.Code Cong. & Ad. News 237, 308, 309. As pointed out in an article analyzing the legislative history of the interim presumption, “[b]y this [Conference Report] statement, the conferees alerted the Secretary of Labor that he was not to treat the interim presumption as irrebuttable.” Solomons, A Critical Analysis of the Legislative History Surrounding the Black Lung Interim Presumption and a Survey of its Unresolved Issues, 83 W.VA.L.REV. 869, 893 (1981). Thus, by statute, the disposition of a black lung claim must be based on all relevant evidence and the presumption which the Secretary was directed to promulgate must be rebuttable. The statute, however, leaves to the Secretary how the presumption is to be triggered and rebutted and how the various burdens of persuasion and production are to be allocated between the claimant and the employer.
The regulation promulgated by the Secretary is divided into two parts. The first part, Part (a), enumerates four distinct medical requirements which, if met, “establish” the interim presumption. The second part of the regulation, Part (b), addresses the requirements for rebutting a presumption which has been established under Part (a). Part (a) by its own terms calls for the presumption to be triggered under (a)(1) by “[a ] chest roentgenogram (x-ray),” and under (a)(4) if “[o]ther medical evidence, including the documented opinion of a physician exercising reasoned medical judgment, establishes the presence of a totally disabling respiratory or pulmonary impairment” (emphasis added). Thus, with respect to these two medical requirements, I can only conclude that a single qualifying x-ray or a single physician’s opinion that a claimant has a disabling pulmonary impairment will clearly suffice to trigger the presumption. Of course, certain minimal requirements of reliability and authenticity must be met, including identification of the physician reading the x-ray or rendering the opinion, the date of the report, and compliance with any applicable quality standards for x-rays found elsewhere in the regulations. See 20 *434C.F.R. §§ 727.206(a), 718.102, 718.104, 410.-428.
Concerning the medical requirements under § 727.203(a)(2) and (a)(3), the regulation employs the terms “ventilatory studies” and “blood gas studies” in the plural. Nevertheless, I conclude that a reasonable interpretation of this language requires the presumption to be triggered if the results of one set of ventilatory or blood gas studies demonstrate values above those listed in the tables.6 I note that this interpretation is fully supported by the regulations which define how ventilatory and blood gas tests are to be conducted. These regulations demonstrate that each pulmonary function study consists of several tests and must be accompanied by two to three tracings of each test performed. 20 C.F.R. §§ 718.103; 410.430. Similarly, a blood gas study may also.have separate components, one reflecting the results obtained at rest, and the other reporting the results of testing during exercise. 20 C.F.R. § 718.-105.
Certainly, I find nothing in Part (a) of the regulation which permits — much less requires — the weighing of conflicting like-kind evidence by the factfinder before triggering^the presumption. In fact, the view espoused by the Director that all evidence must be weighed before invoking the presumption renders the rebuttal phase of the inquiry superfluous. Judge Phillips’ opinion, in finding the Director’s position on this point reasonable, effectively rewrites the rebuttal portion of the regulation and makes the presumption once triggered, at least in part, irrebuttable.7 This interpretation, which renders the regulation internally inconsistent and contradictory, cannot withstand the test of reasonableness under any conceivable criteria. Moreover, insofar as it makes the presumption irrebuttable, it clearly conflicts with congressional intent.
I would accordingly overrule our previous decision in Consolidation Coal Co. v. Sanati, 713 F.2d 480 (4th Cir.1983), which held that the ALJ must weigh conflicting evidence before determining whether the presumption has been triggered. I would hold instead that under the plain meaning of 20 C.F.R. § 727.203(a), the claimant satisfies his initial burden of production if he introduces into evidence one qualifying x-ray, one set of qualifying ventilatory or blood gas studies, or the documented opinion of one physician exercising reasoned medical judgment.8 Contrary to the conclusion reached by Judge Widener. and a majority of this Court that in the absence *435of a physician’s opinion other medical evidence must be weighed before the (a)(4) presumption is triggered, I conclude that a physician’s opinion is an absolute prerequisite to invoking the presumption under (a)(4) and that consequently weighing of the evidence is not appropriate.
Once the claimant’s initial burden has been satisfied and the presumption is triggered, the burden necessarily shifts to the employer to rebut it. Under Part (b) of the regulation, rebuttal of the interm presumption is subdivided into four categories. The presumption is rebutted if the employer establishes that (1) the miner continues in his usual coal mine work or in gainful employment requiring similar skills and abilities; (2) the miner is able to do his usual coal mine work or gainful work requiring similar skills and abilities; (3) the miner’s death or disability did not arise, in whole or in part, out of coal mine employment; or (4) the miner does not have pneumoconiosis. 20 C.F.R. § 727.203(b).
It is in the rebuttal portion of the regulation, after the burden has shifted to the employer, that the Secretary incorporated Congress’ “all relevant evidence” language, requiring that “[i]n adjudicating a claim under this subpart, all relevant medical evidence shall be considered.” 20 C.F.R. § 727.203(b). In my view, placement of this language is not, as the employers argue, awkward or inexact, but entirely appropriate and consistent with congressional intent. For it is after hearing the rebuttal phase of a case where the presumption has been invoked, and determining whether the employer has sustained its burden of proving by a preponderance of the evidence that the claimant does not have pneumoconiosis, or does not otherwise meet the criteria for eligibility found at § 727.203(b)(l)-(b)(4), that the factfinder is in a position to make a final decision on the claim based on the weighing of “all relevant evidence.”
As we concluded in addressing the employer’s rebuttal obligation under § 727.-203(b)(3), in Bethlehem Mines Corp. v. Massey, 736 F.2d 120, 123-24 (4th Cir.1984):
[T]he employer must rule out the causal relationship between the miner’s total disability and his coal mine employment in order to rebut the interim presumption ... The reality of coal mine employment is such that many physical and environmental factors may converge to produce a totally disabling respiratory or pulmonary impairment. The Secretary’s rebuttal regulation acknowledges this reality and, consistent with the letter and spirit of the Black Lung Act and traditional workers’ compensation principles, places the burden on the employer to disprove the causal relationship between coal mine employment and total disability once the claimant establishes the existence of a qualifying medical condition. (emphasis added).
Massey correctly recognized the effect of shifting the burden of persuasion onto the employer once the presumption under § 727.203(a) had been invoked. In Alabama By-Products v. Killingsworth, 733 F.2d 1511, 1514 (11th Cir.1984), the Eleventh Circuit similarly concluded that:
The plain meaning of the regulatory language of 20 C.F.R. § 727.203(b) demonstrates that the burden of persuasion shifts to the employer on rebuttal. Under section 727.203(b), the employer is required to “establish” the elements of rebuttal. “Establish” is clearly synonymous with “prove.” Furthermore, under section 727.203(b), the factfinder must consider “all relevant medical evidence” to determine if the presumption has been rebutted, thus indicating that the factfinder must consider evidence introduced by both sides and that the operator must persuade the factfinder,
(footnote omitted). The Sixth and the Tenth Circuits have likewise concluded that the burden of persuasion under § 727.-203(b) shifts to the employer on rebuttal. Gibas v. Saginaw Mining Company, 748 F.2d 1112, 1120 (6th Cir.1984), cert. denied, — U.S. -, 105 S.Ct. 2357, 86 L.Ed.2d 258 (1985); Kaiser Steel Corporation v. Director, Office of Workers’ Compensation *436Programs, 748 F.2d 1426, 1430 (10th Cir.1984).
This statement of the employer’s rebuttal obligation is, moreover, consistent with the interpretation of the employer’s burden under the fifteen-year statutory presumption. Cf. United States Steel Corp. v. Gray, 588 F.2d 1022, 1028 (5th Cir.1979) (“The statute shifts to the Secretary or to the mine operator the burden of disproving disability due to pneumoconiosis once the claimant makes the threshold showing that he worked fifteen or more years in the mines and suffers a totally disabling respiratory or pulmonary impairment. The burden on the Secretary or operator is then to prove by a preponderance of evidence that the claimant does not suffer pneumoconiosis, as defined by the Act, or that the impairment is not connected with his employment in the mines.”)9
Neither the statute nor the regulation addresses the quantum of evidence that constitutes a preponderance of all relevant evidence. To me, however, it is significant that Congress qualified the “all relevant evidence” standard by specifically providing that “no claim for benefits under this part shall be denied solely on the basis of the results of a chest roentgenogram.” 30 U.S.C. § 923(b). Id. Thus, I would find that neither a single negative x-ray nor multiple negative x-rays may constitute the sole basis for denying benefits.10 Furthermore, I would continue to adhere to our holding in Whicker v. U.S. Dept. of Labor Benefits Review Board, 733 F.2d 346, 349 (4th Cir.1984), that “[n]on-qualifying test results ... cannot be used as the principal or exclusive means of rebutting an interim presumption of pneumoconiosis” under 20 C.F.R. § 727.203(b) (emphasis added). To hold otherwise would, as we noted in Whicker, defeat “the specific language and purposes of the applicable regulations.” Id. Nevertheless, I agree that non-qualifying test results may be part of the rebuttal inquiry under the “all relevant evidence” standard, and are particularly relevant when they are given a detailed interpretation by an examining physician in reaching a medical conclusion as to a claimant’s impairment.
In summary, I conclude that in a black lung case involving use of the interim presumption in Part C claims, the claimant has the initial burden of producing evidence which meets one of the medical requirements listed in § 727.203(a)(1) through (a)(4), i.e. one positive x-ray, one qualifying set of ventilatory or blood gas studies, or one physician’s opinion. Of course, the evidence submitted by the claimant to trigger the presumption must conform to pertinent standards for quality and authenticity. Once the initial burden is satisfied, I would find that the burden of persuasion shifts to the employer, who then must prove by a preponderance of evidence that the claimant does not have pneumoconiosis, or that he continues to perform or is capable of performing his usual coal mine work, or that the impairment is not connected with his employment in the mines.
In deciding whether the presumption has been rebutted, and ultimately whether the claimant is entitled to black lung benefits, I agree that the factfinder must consider all relevant evidence, but with the proviso that *437(1) a claim may not be denied solely on the basis of any negative x-ray and (2) non-qualifying test results may not be the primary or exclusive means of rebutting the presumption.
In applying these views to the facts of the three cases before us, I conclude as follows:
1. Stapleton
I would find that in Stapleton’s case the ALJ correctly concluded that the 1976 positive x-ray was sufficient to invoke the interim presumption under (a)(1). Moreover, I would find that the presumption was also triggered under (a)(2) by the positive ventilatory study. Nevertheless, I would affirm the Board’s denial of benefits on the ground that there is substantial evidence to demonstrate that the presumption was sufficiently rebutted. This evidence included the reports of Stapleton’s treating physician and other examining physicians that claimant suffered from a cardiac disability rather than from a pulmonary impairment.
2. Ray
In Ray’s case, I cannot accept appellant’s contention that the presumption was triggered under (a)(1) by the 1974 positive x-ray. This x-ray was not sufficiently identifiable to meet the regulatory requirements for an x-ray under 20 C.F.R. § 718.-102(c), which provides, inter alia, that “[t]he report shall specify the name and qualifications of the person who took the film and the name and qualifications of the physician interpreting the film.” I would find, however, that because of the two qualifying ventilatory studies and the opinion of at least one physician that Ray was totally disabled due to a respiratory impairment, the presumption was triggered under (a)(2) and (a)(4). Because the AU incorrectly concluded that the presumption was not invoked, I would remand this case for a determination of whether the presumption was rebutted.11
3. Mullins
I would find that there was sufficient evidence to invoke the presumption on behalf of the claimant, Cornett, under (a)(1), (a)(2), (a)(3), and (a)(4). Furthermore, I would affirm the Board’s decision granting benefits on the ground that it is supported by substantial evidence and that the employer did not meet its rebuttal obligation.
As stated in the per curiam opinion summarizing the results in these cases, the award of benefits to Cornett is affirmed. However, in accordance with Part III. B. of this opinion, infra, in which all the judges have joined, that portion of the decision below which awarded interest on Cornett’s claim back to July, 1978, is reversed and the case is remanded with directions that an appropriate award of interest be entered to commence thirty days after the date of the initial determination of eligibility.
B. Pre-judgment Interest
The interest regulation at issue in Mullins, 20 C.F.R. § 725.608(a) (1979), provides that:
If an operator or other employer fails or refuses to pay any or all benefits due under the terms of an initial determination by a deputy commissioner (§ 725.-420), a decision and order filed and served by an administrative law judge (§ 725.478) or a decision filed by the Board or a United States court of appeals, including any penalty awarded in addition to benefits in accordance with § 725.607, such operator shall be liable for 6 percent simple annual interest on all past due benefits computed from the date on which such benefits were due and payable____
(Emphasis added).
The Director interprets the regulation to provide for the assessment of interest only *438from the date thirty days after the first favorable decision, whether made by the Deputy Commissioner in an initial determination, or by an ALT, the Board, or a court of appeals. The Board has rejected the Director’s interpretation and, as in this case, has construed 20 C.F.R. § 725.608(a) to provide for the assessment of interest from the date of a claimant’s eligibility under the Act, i.e., from the due date of any retroactive payment to which a claimant ultimately becomes entitled under a decision awarding benefits.
On appeal, Mullins and the Director contend that the Director’s interpretation must be accorded deference and that the Board’s substitution of its own interpretation of the interest regulation constitutes improper rulemaking and is erroneous as a matter of law. We agree.
The “common law rule is that the one who owes a sum of money at a date certain is obliged to pay interest for withholding payment.” Howmet Aluminum Corp. v. Hartford Accident & Indemnity Co., 665 F.2d 476, 479 (3d Cir.1981). Thus, as a general rule, interest may be awarded only for the wrongful withholding of payment on a liquidated claim, after the payment obligation arises. Milgo Electronic Corp. v. United Business Communications, Inc., 623 F.2d 645, 667 (10th Cir.), cert. denied, 449 U.S. 1066, 101 S.Ct. 794, 66 L.Ed.2d 611 (1980); New York Shipping Ass’n v. Federal Maritime Commission, 571 F.2d 1231, 1242 (D.C.Cir.1978).12
Moreover, although there was no statutory provision regarding interest on benefit awards until 1981, the 1981 amendments, adopted the Director’s interpretation. 30 U.S.C. § 932(d) now provides that:
With respect to payments withheld pending final adjudication of liability in the case of claims filed on or after the effective date of the Black Lung Benefits Amendments of 1981 [January 1, 1982], such interest shall commence to accumulate 30 days after the date of the determination that such an award should be made.
We have held that “later acts of Congress should be accorded ‘significant weight’ in determining the intent of earlier legislation.” Director, OWCP v. National Mines Corp., 554 F.2d 1267, 1275 (4th Cir.1977), quoting NLRB v. Bell Aerospace Co., 416 U.S. 267, 275, 94 S.Ct. 1757, 1762, 40 L.Ed.2d 134 (1974). The Board, however, rejected the Director’s interpretation as the interpretation intended by Congress, relying (1) upon the position taken by the Director on the interest question in an earlier case, Honaker v. Jewell Ridge Coal Corp., 2 BLR 1-947 (Benefits Review Board, 1980), aff’d on other grounds mem. sub. nom. Jewell Ridge Coal Corp. v. Honaker, 649 F.2d 863 (4th Cir.1981); (2) upon the decision of this Court in Clinchfield Coal Co. v. Cox, 611 F.2d 47 (4th Cir.1979); and (3) upon case law developed under the Longshoremen’s and Harbor Workers’ Compensation Act, 33 U.S.C. § 901 et seq., many of the provisions of which are incorporated into the Black Lung Benefits Act. We agree with Mullins and the Director that the Board’s reliance was misplaced.
The claims in Cox and Honaker were processed and approved in accordance with the Black Lung Benefits Act of 1972, under which no interest regulation had been promulgated. Section 725.608(a), first promulgated in 1978 to implement the 1978 Amendments, was inapplicable to those claims. Neither the regulation nor the Director’s interpretation of that regulation was at issue in either case. We hold, therefore, that the Board erred in relying on Cox and the Director’s position in Honaker *439to reject the Director’s interpretation of 20 C.F.R. § 725.608(a) in the instant case. Udall v. Tallman, 380 U.S. 1, 16, 85 S.Ct. 792, 801, 13 L.Ed.2d 616 (1965).
The Board also erred in relying on the Longshoremen’s Act. Interest under the Longshoremen’s Act, like interest under the Director’s interpretation of 20 C.F.R. § 725.608(a), accrues only from the date that an employer first incurs a payment obligation for a liability on a disability claim. Cf. 33 U.S.C. § 914(b), 918 and Strackan Shipping Co. v. Wedemeyer, 452 F.2d 1225 (5th Cir.1971), cert. denied, 406 U.S. 958, 92 S.Ct. 2060, 32 L.Ed.2d 344 (1972) with 20 C.F.R. § 725.522(a). Given that fact, the Director’s interpretation of 20 C.F.R. § 725.608(a) comports with the manner in which interest is awarded under the Longshoremen’s Act.
Even assuming otherwise, however, we conclude that the Board erred in relying on the Longshoremen’s Act to interpret 20 C.F.R. § 725.608(a). As this Court stated in National Mines Corp., supra, “[t]he Black Lung Act does not inflexibly incorporate every provision of the Longshoremen’s Act.” 554 F.2d at 1273. Instead, “Title 30 U.S.C. § 932(a) specifically states that the provisions of the Longshoremen’s Act shall be applicable ‘except as the Secretary shall by regulation otherwise provide.’ ” Id. This indicates a “congressional intention to empower the Secretary to depart from specific requirements of the Longshoremen’s Act in order to administer the black lung compensation program properly.” Id. at 1274. Thus, the Board’s review of the Director’s interpretation of 20 C.F.R. § 725.-608(a) was governed not by the Longshoremen’s Act, but, instead, by the Black Lung Benefits Act.
For the foregoing reasons, we uphold the Director’s interpretation of the interest regulation as reasonable and find that interest shall accrue only from the date beginning thirty days after the first agency decision awarding black lung benefits. We accordingly reverse that portion of the decision in Mullins which awarded interest as of July 1, 1978.13
I am authorized to say that HARRISON L. WINTER, SPROUSE and SNEEDEN, JJ., join in this opinion.
. See, e.g., Whicker v. U.S. Dept. of Labor Benefits Review Board, 733 F.2d 346 (4th Cir.1984), Consolidation Coal Co. v. Sanati, 713 F.2d 480 (4th Cir.1983), and Hampton v. U.S. Dept. of Labor Benefits Review Board, 678 F.2d 506 (4th Cir. 1982).
. A "B" reader is a physician who has completed a course and passed a proficiency examination conducted by the National Institute for Occupational Safety and Health for reading pneumoconiosis on x-ray films.
. The brief submitted by Mullins in this appeal informs us that Cornett died on June 22, 1983, from acute congestive heart failure.
. 30 U.S.C. § 902(f) provides as follows:
(1) The term "total disability” has the meaning given it by regulations of the Secretary of Health and Human Services for claims under Part B of this subchapter, and by regulations of the Secretary of Labor for claims under part C of this subchapter, subject to the relevant provisions of subsections (b) and (d) of section 923 of this title, except that—
(A) in the case of a living miner, such regulations shall provide that a miner shall be considered totally disabled when pneumoconiosis prevents him or her from engaging in gainful employment requiring the skills and abilities comparable to those of any employment in a mine or mines in which he or she previously engaged with some regularity and over a substantial period of time.
(B) Such regulations shall provide that (i) a deceased miner's employment in a mine at the time of death shall not be used as conclusive evidence that the miner was not totally disabled; and (ii) in the case of a living miner, if there are changed circumstances of employment indicative of reduced ability to perform his or her usual coal mine work, such miner's employment in a mine shall not be used as conclusive evidence that the miner is not totally disabled;
(C) such regulations shall not provide more restrictive criteria than those applicable under section 423(d) of Title 42; and
(D) the Secretary of Labor, in consultation with the Director of the National Institute for Occupational Safety and Health, shall establish criteria for all appropriate medical tests under this subsection which accurately reflect total disability in coal miners as defined in subparagraph (A).
(2) Criteria applied by the Secretary of Labor in the case of—
(A) any claim which is subject to review by the Secretary of Health and Human Services, or subject to a determination by the Secretary of Labor, under section 945(a) of this title;
(B) any claim which is subject to review by the Secretary of Labor under section 945(b) of this title; and
(C) any claim filed on or before the effective date of regulations promulgated under this subsection by the Secretary of Labor; shall not be more restrictive than the criteria applicable to a claim filed on June 30, 1973, whether or not the final disposition of any such claim occurs after the date of such promulgation of regulations by the Secretary of Labor.
. Permanent criteria, applicable to claims filed after March 31, 1980, are contained at 20 C.F.R. Part 718.
. As with x-ray evidence, ventilatory and blood gas studies must also comply with applicable quality standards. See 20 C.F.R. §§ 206(a), 718.103, 718.105, 410.430.
. According to the construction offered in Judge Phillips’ opinion, once the evidence is weighed and the presumption is triggered, it may be rebutted under § 727.203(b)(l)-(4) unless it was triggered by proof under § 727.203(a)(4) that the claimant had a totally disabling respiratory or pulmonary impairment or unless it was invoked by proof under § 727.203(a)(1) that the claimant has pneumoconiosis. The word “unless" appears nowhere in the regulation. Similarly, under Judge Phillips’ view, invocation of the presumption conclusively, i.e. irrebuttably establishes that the claimant has pneumoconiosis under § 727.203(a)(1), has certain levels of, respiratory or pulmonary impairment under (a)(2) or (a)(3), and is totally disabled by a respiratory or pulmonary impairment under (a)(4).
. I am not persuaded by the contention advanced by the employers and the Director that the Administrative Procedure Act (APA), 5 U.S.C. §§ 554 et seq., requires the presumption to be invoked under a preponderance of evidence standard. To the extent that the APA would normally be applicable on this question, I find that the statutory and regulatory scheme establishing the interim presumption supersedes the APA’s evidentiary requirements.
Nor am I convinced by Judge Phillips' view, that the regulation’s use of the word “establish” in both the triggering and rebuttal portions compels a conclusion that to trigger the presumption the claimant bears the burden of persuasion under a preponderance standard. "Establish," as used in Part (a) simply means that the claimant must prove at least one of the factual prerequisites to invoke the presumption, i.e. one qualifying x-ray, one set of qualifying ventilatory or blood gas studies, or the documented opinion of one physician. As used in Part (b), “establish” means that the employer must prove the facts necessary to rebut the presumption and ultimately to persuade the factfinder that the claimant is not entitled to benefits.
. The fifteen-year rebuttable presumption at issue in United States Steel Corp. v. Gray, 588 F.2d 1022, 1028 (5th Cir.1979), is found at 30 U.S.C. § 921(c)(4).
. The legislative history to the 1972 amendments documents Congress’ special concern over the inadequacy of x-ray technology in diagnosing pneumoconiosis. S.Rep. No. 92-743, p. 12 (1972), U.S.Code Cong. & Admin.News 1972, p. 2305; Usery v. Turner Elkhorn Mining Co., 428 U.S. 1, 31-34, 96 S.Ct. 2882, 2899-2901, 49 L.Ed.2d 752 (1976), United States Steel Corp. v. Gray, 588 F.2d 1022, 1027-28 (5th Cir.1979).
The employers’ and Director’s contention that the presumption must be invoked by a preponderance of like-kind evidence would, with respect to x-rays, in some cases prevent the presumption from ever being triggered and thus subvert the congressional intention not to deny claims on the basis of a negative chest x-ray. This result, which Judge Phillips’ opinion condones, places the regulation in conflict with the authorizing statute and is in and of itself a sufficient ground for finding the Director's interpretation invalid.
. In reviewing the record, I note that the ALJ overlooked the reading of an x-ray dated January 3, 1977, as positive. I would require this x-ray to be evaluated on remand along with the other evidence.
. The reasonableness of this rule, as applied by the Director in his interpretation of 20 C.F.R. § 725.608(a), is illustrated by the circumstances of this case. Cornett’s eligibility date is July 1, 1978. Cornett, however, had terminated his employment with Mullins on April 30, 1976. He waited for more than two years after ceasing work to file a claim for benefits in July, 1978. Another fifteen months passed before Mullins first had knowledge of Cornett’s claim on October 9, 1979. It was not until five months thereafter, on March 22, 1980, that Mullins first incurred liability on the claim, thirty days after the Deputy Commissioner issued his initial determination on February 20, 1980. 20 C.F.R. § 725.522(a) and .530(a).
. We note that the Seventh Circuit has recently reached the same conclusion on this issue in Peabody Coal Company v. Blankenship, 773 F.2d 173, No. 83-2399 (7th Cir.1985).