dissenting.
I concur and join in Part II, Parts HID and E, and Part IV of the majority’s well-crafted opinion. I disagree, however, with *190the majority’s conclusion that the District Court abused its discretion when it credited the EPA’s expert economist and used that expert’s interest rate to calculate ALC’s economic benefit rather than the rate presented by ALC’s expert. The majority writes that the District Court committed clear error because, in applying the EPA’s 12.73% discount rate, the Court so vastly overstated the economic benefit to ALC of its Clean Water Act (“CWA”) violations that it failed to level the economic playing field. In my view, in selecting the 12.73% rate, the District Court acted squarely within its discretionary authority.
I.
Before discussing the discount rate issue and the Court’s exercise of discretion, I think it worth commenting on the proceeding conducted by the District Court. The $8,244,670 penalty imposed on ALC came after a three-day penalty hearing during which the District Court heard testimony from 13 witnesses, 11 live and 2 through depositions. These witnesses included experts on economic benefit, cost avoidance and aquatic toxicology, ALC’s Director of Environmental Affairs, and officials from the United States Coast Guard, the Pennsylvania Fish and Boat Commission and the Pennsylvania Department of Environmental Protection. Expert testimony was submitted by written proffer with live cross-examination. On the subject of economic benefit, the EPA presented testimony from Robert Harris, an economist, who explained how he calculated the 12.73% WACC. ALC presented testimony from Dr. Howard Pifer, who proposed using the 30-day treasury bill rate to determine the value of the money going forward to the penalty payment date. In a 30-page opinion issued after the hearing, the District Court credited the EPA’s expert testimony, concluding that Dr. Pifer’s argument was not supported by the facts and that the WACC offered a reasonable approach because it represented an average of potential investments made by ALC during the time it had use of the funds that it did not spend on compliance. The District Court also followed Dean Dairy’s endorsement of the WACC, as used in Smithfield Foods.
The majority finds fault with the District Court’s analysis, noting that the government’s calculation of the WACC “relied on values that were not ALC-specific.” Maj. Op. at 181. The majority also believes that, rather than using an average such as the WACC, the government should have applied the actual rate it would have cost ALC to raise capital for the years when it was diverting funds that should have gone to pollution control. Therefore, the majority concludes that the District Court erred in using the 12.73% discount rate.
II.
As I see it, the central issue here is whether the District Court abused its discretion in crediting one expert over another when it determined the interest rate. We have noted many times that abuse of discretion is a highly deferential standard of review. And, we have stated, on numerous occasions, that a decision to credit the testimony of one expert witness over another is entitled to deference. See United States v. Universal Rehabilitation Services (PA), Inc., 205 F.3d 657, 665 (3d Cir.2000), quoting General Elec. Co. v. Joiner, 522 U.S. 136, 143, 118 S.Ct. 512, 139 L.Ed.2d 508 (1997), United States v. Mathis, 264 F.3d 321, 335 (3d Cir.2001), Laverdi v. Jenkins Township, 49 Fed.Appx. 362, 364 (3d Cir.2002), Matlin v. Langkow, 65 Fed.Appx. 373, 382 (3d Cir.2003). The Supreme Court has held that a district court’s evaluation of expert testi*191mony is to be accorded “the deference that is the hallmark of abuse-of-discretion review.” General Elec. Co. v. Joiner, 522 U.S. at 143, 118 S.Ct. 512. A district court abuses its discretion when it “bases its opinion on a clearly erroneous finding of fact, an erroneous legal conclusion, or an improper application of law to fact.” LaSalle Nat’l Bank v. First Conn. Holding Group, L.L.C. XXIII, 287 F.3d 279, 288 (3d Cir.2002). Indeed, we have said that “[i]n order to justify reversal, a district court’s analysis and resulting conclusion must be ‘arbitrary or irrational.’ ” United States v. Universal Rehabilitation Services (PA), Inc., 205 F.3d 657, 665 (3d Cir.2000), quoting In re Paoli R.R. Yard PCB Litig., 113 F.3d 444, 453 (3d Cir.1997) (internal quotations omitted). Abuse of discretion requires a showing of clear error, not inappropriateness. In my view, given our highly deferential standard of review, the District Court did not clearly err in crediting the government’s witness over ALC’s witness and adopting the WACC to calculate economic benefit.
Here, after considering all of the testimony, the District Court credited the testimony of the government’s economic expert concerning the WACC, stating that it “represents the rate of return a company must earn annually to continue to attract its current investors and maintain its current levels of operations. It is a rate which is commonly used by companies in making capital budgeting decisions.” 187 F.Supp.2d at 440, quoting Harris Proffer at 6 (internal quotations omitted); App. I at 47. The District Court also credited the testimony of the government’s expert on avoided costs, noting that he had 30 years of experience in the environmental field, including working for and as a consultant to the EPA and several major steel companies. 187 F.Supp.2d at 437; App. I at 41-42. The District Court was not required to explore every possibility. As the Supreme Court has stated, a district court need not have conducted an “exhaustive search” of all possible alternatives. See, e.g., Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 597, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993); see also Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 147, 119 S.Ct. 1167, 143 L.Ed.2d 238 (1999) (extending Daubert’s gatekeeping obligation to all expert testimony).
Still, the majority conducts a protracted survey of economic theories, considers treatises not specifically presented by experts before the District Court, and decides that it disagrees with the District Court’s discretionary determination. Of course, there will always be disagreement among experts concerning scientific, or in this case economic, theories. However, it is for the District Court Judge, as fact finder, to resolve those disagreements by judging the credibility of the expert witnesses, resolving the conflicting evidence, and assessing the weight of the expert’s testimony. There is nothing in the record here to indicate that the government’s expert did not use sound methodology and adequately support his opinion, and nothing to show that the District Court was clearly erroneous in crediting that opinion.
The majority’s disagreement as to which interest rate is more “appropriate” is not enough to justify a remand.19 This is especially true in light of Dean Dairy, where we stressed that economic benefit “may not be capable of ready determination,” and we accorded “the district court’s *192award of a penalty wide discretion, even though it represents an approximation.” 150 F.3d at 264, citing Tull v. United States, 481 U.S. 412, 426-27, 107 S.Ct. 1831, 95 L.Ed.2d 365 (1987). Surely the choice to credit the government’s expert over ALC’s falls within this wide discretion. Indeed, the Dean Dairy Court went on to say that the “[p]reeise economic benefit to a polluter may be difficult to prove” and that “Reasonable approximations of economic benefit will suffice.” 150 F.3d at 264, quoting Public Interest Research Group of N.J., Inc. v. Powell Duffryn Terminals, Inc., 913 F.2d 64, 80 (3d Cir.1990). As here when the District Court credited one expert’s reasonable approximation of the economic benefit over another’s, it acted well within its discretion. We ought not substitute our own opinion for that of the District Court’s.
In its attempt to fault the District Court’s calculation of the WACC for “rely[ing] on values that were not ALC-specifíc” [ie., using theoretical yields on bonds issued rather than actual yields], the majority, in fact, concedes that the District Court’s analysis contained reasonable approximations. Maj. Op. at 181. It states that while the bond-yield “figure might well have been a reasonable approximation of ALC’s bonds’ yields, a more accurate calculation could easily have been achieved by using figures specific to ALC’s bonds.” Id. However, as long as the District Court’s calculation was “reasonable,” we cannot find the Court to have abused its discretion. Relying on theoretical values rather than actual values to calculate the WACC does not render the District Court’s decision “unsupported,” as the majority contends.
The record shows that the government’s expert gave a satisfactory explanation for his decision to use the WACC in this case instead of, for example, the marginal or current cost of capital for the relevant years, as the majority suggests. He stated:
[The WACC] is a rate that I consider proper and represents a rate that falls between the risk free rate and the equity rate. The reason that I believe that the WACC rate is appropriate is because a company’s cash is fungible. That is, funds are not segregated and used for specific purposes. Funds are used in many different ways and the company receives different returns for each use. Some projects earn a high rate of return. Others earn a low or no rate of return. It is impossible to say exactly how the funds that should have been spent in this example were used. Therefore, I believe the most appropriate rate to use is the average return the company earns on all of its projects. In essence, this is the average return for the company.
App. IV at 1009. The record evidence clearly shows that the District Court’s decision to use the WACC was supported by various considerations, including, as testified by the government’s expert, the fungi-bility of a company’s funds and the variable rates of return a company receives depending on how it uses those funds.
Further, the Court’s exercise of discretion is supported by the case law. Dean Dairy cites the Smithfield Foods Court’s use of the WACC favorably, indicating that the WACC is a perfectly acceptable interest rate for a district court in this circuit to adopt when calculating economic benefit. 150 F.3d at 266, citing United States v. Smithfield Foods, Inc., 972 F.Supp. 338, 349 (E.D.Va.1997).
The majority’s failure to find clear error after combing the record is evident in several places. For example, the majority criticizes the government’s expert’s use of the arithmetic mean (instead of the geome-*193trie mean) to compute an estimate of the WACC for the years 1990-1998. Although the majority admits that “any correction will be slight,” the WACC comes to 12.71%, as opposed to 12.73%, when it is calculated using the geometric mean. Maj. Op. at 183 n. 14. Surely, a discretionary choice by a district judge that results in an interest rate .02% higher than an alternative cannot be viewed as clearly erroneous.
The majority also criticizes the government’s use of a mean interest rate at all, asserting that it “wound up hurting ALC.” Maj. Op. at 184. I do not agree that this calculation unduly punished ALC. Taking an average of the interest rates for all of the years in which ALC was non-compliant is a common and perfectly acceptable method for arriving at a single figure to use when calculating ALC’s economic benefit during those years. I disagree with the majority’s contention that “[t]he theoretical WACC figures from the early 1990s ... really have no bearing on the economic benefit conferred by post-1992 violations” simply because they are the highest figures of the group. Maj. Op. at 184. The figures from 1990 to 1992 are equally as relevant as those from 1993 to 1998, as CWA violations occurred in each of the years from 1990 to 1998. There is no record support for the majority’s assertion that the WACC figures from the early 1990s are “less-relevant” than those for later years. Id. Therefore, the majority’s suggestion that the average WACC was unduly biased towards high numbers is inaccurate.20 Further, the District Court pointed out that, in some instances, it credited the government’s expert in ways that wound up benefitting ALC. For example, in calculating the economic benefit that ALC enjoyed by spending less money to staff its facilities, the District Court noted that the government’s expert
made two assumptions that were favorable to defendant. First, he included in ALC’s actual staffing costs time billed by maintenance workers who stopped by the facility, even though having a maintenance worker stop by is not the same as having full-time staffing. Second, [his] calculations do not include money saved by ALC at its West Leechburg and Brackenridge facilities prior to entry of the consent agreements with Pa-DEP [Pennsylvania Department of Environmental Protection],
187 F.Supp.2d at 437 n. 7, citing Amendola Proffer at 17; App. I at 41. Also, in calculating the least costly upgrade that would have brought ALC into compliance at its Vandergrift facility before 1994, the District Court noted that
the United States might have pointed to a $1.8 million upgrade considered by ALC in 1988 and 1989, or the entire cost of the $5.7 million upgrade of the Van-dergrift WWTP [Wastewater Treatment Plants], and argued that money should have been spent in 1990, rather than 1994. But in an approach that is favorable to ALC, [the government’s expert] calculated the least costly upgrade in 1994 that would likely have eliminated the violations, and provided a $600,000 alternative.
187 F.Supp.2d at 439, citing Amendola Proffer at 12-13; App. I at 44. As with its WACC calculation, the District Court exercised its discretion here and supported its decision with acceptable explanations. Here, however, it arrived at a figure that *194benefited ALC. The majority fails to explain how this decision falls within the District Court’s discretion while its WACC calculation does not.
The majority also hypothesizes that the WACC may not have been as appropriate an approximation of economic benefit for ALC as it was for the company in Smith-field Foods because of differences in the volatility of the industries in which each company operated. Again, the standard of review is abuse of discretion, and not whether another decision might have been more “appropriate.” Further, the majority cites no authority for the proposition that using a theoretical interest rate as opposed to an actual one in a particular industry is clearly erroneous. The majority quotes Chesapeake Bay Found., Inc. v. Gwaltney of Smithfield, Ltd., 611 F.Supp. 1542, 1559 (E.D.Va.1985), as stating that “[t]he actual interest rate Gwaltney itself paid on borrowed funds ... is a more accurate basis for determining Gwaltney’s economic benefit from delay.” Maj. Op. at 182 (ellipsis in original). When put into context, however, this case does not support the majority’s position. In Gwaltney, the plaintiffs calculation computed Gwalt-ney’s economic benefit from delay using “the ten-year rate of return on equity earned by Smithfield Foods, Inc. — Gwalt-ney’s parent corporation.” 611 F.Supp. at 1559. The Court went on to hold that “[a]t least in these circumstances, the Court believes that 13% — the actual interest rate Gwaltney itself paid on borrowed funds — is a more accurate basis for determining Gwaltney’s economic benefit from delay.” Id. The Gwaltney Court, therefore, held against the use of a parent corporation’s interest rate, but not the use of a theoretical interest rate per se. In addition, the record shows that the District Court did consider the economic benefit calculation in an industry-specific context, stating that “[failures to comply with the [CWA] can ... result in indirect competitive benefits when compared with companies in the same field that do comply with the [CWA].” 187 F.Supp.2d at 436; App. I at 40.
Finally, the majority asserts that the District Court abused its discretion in choosing the WACC instead of a lower alternative interest rate because using the WACC evidenced an effort to punish and deter when calculating the economic benefit. However, the District Court clearly recognized that there are two steps to the “bottom up” approach to penalty assessment and it is the second step that is geared toward punishing and deterring the violator. The District Court stated:
To achieve the goal of deterrence, an appropriate penalty must encompass both the economic benefit that the defendant obtained through its noncompliance, and an additional punitive component that takes into account the penalty factors listed in Section 1319(d). Without the second component, those regulated by the CWA would have nothing to lose by violating it.
187 F.Supp.2d at 439; App. I at 54. The District Court was clearly mindful of the two-step process to be used when assessing penalty, first calculating the economic benefit and then considering the penalty factors to increase that figure. The Court followed the correct analysis, only taking punitive measures in the second step when it doubled the economic benefit figure. Despite the majority’s contention to the contrary, the District Court demonstrated a proper application of the law in assessing the penalty and, therefore, did not abuse its discretion.
In short, there is nothing in the record to show that the District Court committed clear error in its choice of the interest rate to calculate economic benefit. After carefully weighing the evidence presented by *195experts on both sides during a three-day penalty trial, the District Court exercised its discretion as the trier of fact and credited the testimony of one witness over another. The decision is supported by the expert testimony as well as our case law. Because I do not believe that the District Court’s fact-finding was clearly erroneous, its decision is entitled to deference under abuse of discretion review.
I would, therefore, affirm the District Court’s decision as to the interest rate used to calculate economic benefit.
. The majority states, for example, that "[i]n commenting upon the cost-of-capital measure adopted by the District Court [x.e., the WACC], we hope to provide some guidance as to what constitutes an appropriate cost-of-capital measure of economic benefit.” Maj. Op. at 181.
. The majority also overstates the degree to which the highest figures deviate from the rest of those in the calculation. A figure of 15.85% would not be considered a statistical outlier when computing an average, particularly when the same figure appears twice and the rest of the figures range from 10.53% to 13.95%.