The United States Customs Service (“Customs”) appeals the judgment of the Court of International Trade granting-summary judgment in favor of SL Service, Inc. (“SL Service”).1 SL Serv., Inc. v. United States, 244 F.Supp.2d 1359 (Ct. Int’l Trade 2002). Because the Court of International Trade erroneously applied Texaco Marine Services, Inc. v. United States, 44 F.3d 1539 (Fed.Cir.1994) (“Texaco ”), we reverse.
Background
Between November 22 and December 1, 1995, the Sea-Land Pacific, a ship owned by SL Service, was dry-docked at the Hongkong United Dockyards for the purpose of obtaining American Bureau of Shipping and United States Coast Guard required inspections and modifications, which are non-dutiable, in addition to dutiable repairs. Upon returning to the United States, Customs assessed a duty pursuant to 19 U.S.C. § 1466(a), which states that “[t]he equipments, or any part thereof, including boats, purchased for, or the repair parts or materials to be used, or the expenses of repairs made in a foreign country upon a vessel documented under the laws of the United States ... shall ... be liable to entry and the payment of an ad valorem duty ... on the cost thereof in such foreign country.” (emphasis added).
As part of this assessment, Customs determined that the cost of dry-docking should be considered an “expense of repair” because-it was necessitated by the dutiable repairs as well as the non-dutiable inspections and modifications. Customs did not, however, impose the 50% ad valo-rem duty on the full cost of dry-docking. Instead, it determined that only that portion of the cost of dry-docking attributable to the dutiable repairs should be used to calculate the duty. This amount was determined by dividing the cost of dutiable repairs by the sum of the cost of dutiable and non-dutiable work. The cost of dry-docking' was then multiplied by this fraction, resulting in an estimation of the cost of dry-docking due to the dutiable repairs. The 50% ad valorem duty was applied to this amount.
After having timely protested the liquidation to Customs, SL Service brought this challenge in the Court of International Trade claiming that the duty imposed on dry-docking violated the “but for” test prescribed by Texaco and that the apportionment technique was contrary to section 1466(a). In addition, SL Service argued that Customs violated 19 U.S.C. § 1625(c) by failing to provide notice and receive *1360comment about the use of apportionment. Having stipulated that the Sea-Land Pacific was dry-docked for no longer than necessary to complete the non-dutiable inspections and modifications, both parties moved for summary judgment.
The Court of International Trade granted summary judgment in favor of SL Service. It found that Texaco delineated two categories of expenses for the purpose of 19 U.S.C. § 1466(a). The first category, considered “expenses of repairs” and therefore dutiable, would not be incurred “but for” the undertaking of dutiable repairs. The second category, non-dutiable expenses, referred to those expenses incurred for the purpose of obtaining only non-dutiable inspections and modifications as well as those required by both dutiable and non-dutiable work (“dual-purpose expenses”). Based on this reading of Texaco, the court determined that the duty was arbitrary, capricious and in violation of the law because the dry-docking of the Sea-Land Pacific was necessitated by both non-dutiable and dutiable work. As such, it was a dual-purpose expense not subject to section 1466(a).
On appeal, Customs contends that the Court of International Trade’s interpretation of Texaco is too narrow and in contravention of the language and purpose of 19 U.S.C. § 1466(a). Customs claims that the holding in Texaco applies only to expenses incurred as the result of either non-dutiable or dutiable work (“single-purpose expenses”), but not to dual-purpose expenses. Further, it argues that section 1466(a), a statute enacted to protect the domestic shipbuilding and repair industry, should not be interpreted in a manner that would allow artful ship-owners to avoid virtually all duties on expenses of foreign repairs.
Discussion
This case raises two questions: (1) whether dry-docking that is required by both dutiable and non-dutiable work is an “expense of repair”; and (2) whether Customs’ use of apportionment is permissible. With respect to both, we answer in the affirmative.
We review a grant of summary judgment by the Court of International Trade de novo. New Zealand Lamb Co., Inc. v. United States, 149 F.3d 1366, 1367 (Fed.Cir.1998). Summary judgment is appropriate when “there is no genuine issue as to any material fact and the moving party is entitled to judgment as a matter of law.” Ct. Int’l Trade R. 56(c); Fed.R.Civ.P. 56(c).
1. The crux of the error below was the court's misinterpretation and resulting misapplication of Texaco, in which we were asked to decide whether “cleaning performed subsequent to dutiable repairs ... [and] ... work associated with protective coverings used during dutiable repairs” were “expenses of repairs” and, therefore, dutiable. 44 F.3d at 1541. We determined that the expenses at issue were dutiable because they would not have been incurred “but for” dutiable repairs. Id. at 1544. In so holding, we announced the following test: “expenses of repairs” covers all expenses “which, but for dutiable repair work, would not have been incurred.” Id.
The most obvious difference between the facts here and those in Texaco is that Texaco dealt with single-purpose expenses while the dry-docking of the Sea-Land Pacific was a dual-purpose expense. As such, the “but for” test, which was formulated for classification of single-purpose expenses, is inapplicable. SL Service counters that Texaco did, in fact, “consider” dual-purpose expenses. It relies on a footnote in Texaco, which states
*1361Although it appears that some cleaning of the cargo tanks to prepare them to carry cargo would have been necessary even if the repairs had not been made, it also is true that all the debris mentioned in the invoice was created by the repairs. In this regard, the invoice does not indicate that the cleaning included the cleaning of the remains of previous cargo. In any event, Texaco has made no effort to separate from the total G-2(g) expenses amounts that would have been incurred to clean the cargo tanks as a normal maintenance service had the G-2 repairs not been made.
44 F.3d at 1548 n. 9. SL Service extrapolates from this that we specifically considered dual-purpose expenses because we noted that the petitioner in Texaco could have differentiated the expenses at issue but chose not to. Our observation, however, did nothing to change the nature of expenses at issue, all four of which were single-purpose expenses. Id. at 1541-42. It is irrelevant to our determination of the dutiability of dual-purpose expenses that Texaco could have argued that the cleaning expenses were necessitated by both dutiable and non-dutiable work. The prec-edential force of Texaco applies only to single-purpose expenses. This is equally true with respect to Sea-Land Service, Inc. v. United States, 239 F.3d 1366 (Fed.Cir.2001), because it addressed the same type of expenses considered by Texaco.
SL Service also submits that the discussion in Texaco of United States v. Geo Hall Coal, 142 F. 1039 (2d Cir.1906), establishes that the “but for” test applies to dual-purpose expenses. 44 F.3d at 1545-46. According to SL Service, the section referring to Geo Hall Coal held that dry-docking was not a dutiable expense when it is required by non-dutiable inspections and modifications. This contention, however, is not supported by either case.
First, there is no evidence that the dutiable repairs in Geo Hall Coal required dry-docking. The only information available to us now, or in Texaco, was contained in an unpublished opinion of the Department of Treasury Board of General Appraisers, which did not specify the type of dutiable repairs performed or whether they necessitated dry-docking. The decision stated only that dry-docking is not always an expense of repairs because dutiable repairs are made. For instance, dry-docking may be required by the inspections and modifications, but not by the dutiable repairs. Therefore, it is just as likely that the outcome in Geo Hall Coal is consistent with our holding here. Second, Geo Hall Coal addressed a jurisdictional question only. 134 F. 1003 (S.D.N.Y.1905), aff'd, 142 F. 1039 (2d Cir.1906). There were no findings with respect to the dutiability of dry-docking. Finally, the discussion in Texaco is consistent with the fact that the dutiable repairs in Geo Hall Coal did not require dry-docking. 44 F.3d at 1545-46. According to Texaco, “the board held that the dry-docking expense was not subject to the vessel repair duty because the board found that the expense would have been incurred irrespective of whether or not dutiable repairs were performed.” Id. at 1546. This does not imply, as SL Service contends, that dry-docking is never dutiable when required by non-dutiable inspections and modifications. It merely reiterates that the dry-docking in Geo Hall Coal was required by the inspections and modifications and would have been needed whether or not the dutiable repairs, which did not necessarily require dry-docking, were performed.
The well-developed history of the “but for” test instructs that special treatment is required when concurrent and independently sufficient acts combine to cause harm. See W. Page Keeton et al., Prosser and Keeton on The Law of Torts § 41, at *1362266 (5th Ed.1984). In one such scenario, two negligently caused fires merged and destroyed a plaintiffs property. See McClellan v. St. Paul, M & M R. Co., 58 Minn. 104, 59 N.W. 978 (1894); Dan B. Dobbs, The Law of Torts § 171, at 414 (2000). “[A] literal and simple version of the but-for test holds that neither defendant’s act is a cause of the harm.” Dobbs § 171, at 414. Such a result, however, has been universally condemned as “violating both an intuitive sense of causation and good legal policy.” Id. § 171, at 415; see also Restatement (Third) of Torts: Liability for Physical Harm § 27 (Tentative Draft No. 2) (“[C]ourts have long imposed liability when a tortfeasor’s conduct, while not necessary for the outcome, would have been a factual cause if the other competing causal set had not been operating.”).
The non-dutiable inspections and modifications and the dutiable repairs are analogous. In the same sense that each fire was responsible for the damage, the dry-docking was equally caused by both the non-dutiable and dutiable work. And just as the tortfeasor in concurrent causation cases is held responsible for the harm he causes, it is rational to consider the dry-docking an “expense of repairs.”
Texaco did not hold that dry-docking is always non-dutiable when required by inspections and modifications. In fact, there is no basis upon which to contend that it even considered dual-purpose expenses. Dry-docking-that is required by dutiable repairs is, therefore, rightly considered an “expense of repairs” and is subject to 19 U.S.C. § 1466(a).
2.' SL Service next argues that Customs’ method of apportionment is contrary to 19 U.S.C. § 1466(a). According to SL Services’ line of reasoning, apportionment is illegal because the imposition of a duty on dry-docking violates the “but for” test. This argument, of course, simply relies on its primary contention that dual-purpose dry-docking is not dutiable. However, apportionment is consistent with section 1466(a) and the “but for” test. In the context of dual-purpose expenses, it is rational to impose the duty on only that portion of the expense that is fairly attributable to the dutiable repairs. Indeed, to impose the 50% ad valorem duty on the entire cost of dry-docking in this case would exceed the mandate of the statute. The logical appeal of apportionment has been recognized in other areas of the law. In tort law, “apportionment may be made on the ground that one defendant caused a particular loss or an identifiable share of the loss and should be liable for no more.” Dobbs § 170, at 413.
In addition, apportionment has been used by Customs for some time and is, therefore, entitled to deference. See Zenith Radio Corp. v. United States, 437 U.S. 443, 98 S.Ct. 2441, 57 L.Ed.2d 337 (1978); see also Brown v. Gardner, 513 U.S. 115, 122, 115 S.Ct. 552, 130 L.Ed.2d 462 (1994); Toyota Motor Sales, U.S.A., Inc. v. United States, 585 F.Supp. 649, 7 C.I.T. 178, 192 (1984), aff'd, 753 F.2d 1061 (Fed.Cir.1985) (“In interpreting a statute a long-standing administrative practice is entitled to deference by the courts, even where, as here, judicial review is de novo.”). As evidence of its practice, Customs provided three letters documenting the use of apportionment in the liquidation of vessel repair entries. In' all three letters the cost of obtaining a gas free certificate was apportioned between the dutiable repairs and non-dutiable work. Customs explained in the letter dated March 31, 1993:
The costs associated with obtaining a Gas Free Certificate constitute ordinary and necessary expenses incident to repair operations and are thus dutiable. In liquidating these charges, such charges are to be apportioned between the costs which are to be remitted and *1363those for which relief is not warranted, and duty assessed on that portion of the charges applicable to items which are not being remitted. In the present case, as the certificates related to inspections, they should be pro-rated accordingly.
Customs’ long-standing practice of apportioning the cost of various expenses between dutiable repairs and non-dutiable inspections and modifications comports with both the statute and common sense.
Finally, SL Service contends that Customs’ use of apportionment had the effect of modifying either prior rulings or “the treatment previously accorded ... to substantially identical transactions,” and, therefore, triggered 19 U.S.C. § 1625(c). As evidenced by the “Customs Information Exchange” letters, however, Customs has used apportionment in the context of section 1466(a) for more than 40 years. Because apportionment is an established agency practice, its use does not constitute the revocation or modification of a previous ruling or treatment, and therefore section 1625(c) is inapplicable.
Conclusion
Accordingly, the judgment of the Court of International Trade is reversed. REVERSED.
. On November 9, 1999, the Court of International Trade designated this case a test case. SL Serv., 244 F.Supp.2d at 1360.