PUBLISH 

UNITED STATES COURT OF APPEALS 

FOR THE TENTH CIRCUIT 

_________________________________ 

SAMANTHA HALL, 

 Plaintiff - Appellant, 

v. 

CONOCO INC.; 

CONOCOPHILLIPS COMPANY; 

PHILLIPS 66 COMPANY, 

 Defendants - Appellees. 

No. 17-6086 

_________________________________ 

Appeal from the United States District Court 

for the Western District of Oklahoma 

(D.C. No. 5:14-CV-00670-HE)

_________________________________ 

Jason B. Aamodt of Indian & Environmental Law Group, PLLC, Tulsa, 

Oklahoma (Krystina E. Phillips, Dallas L.D. Strimple, of Indian & 

Environmental Law Group, PLLC, Tulsa, Oklahoma; Trae Gray, Ryan 

Ellis, of LandownerFirm, PLLC, Coalgate, Oklahoma; G. Steven Stidham 

of Levinson, Smith & Huffman, P.C., Tulsa, Oklahoma, with him on the 

briefs), for Plaintiff-Appellant. 

Brett J. Young (Joy M. Soloway, Katherine D. Mackillop, Devin Wagner, 

with him on the brief), of Norton Rose Fulbright US LLP, Houston, Texas, 

for Defendants-Appellees. 

_________________________________ 

Before BACHARACH, MURPHY, and McHUGH, Circuit Judges. 

_________________________________ 

BACHARACH, Circuit Judge. 

_________________________________ 

FILED 

United States Court of Appeals 

Tenth Circuit 

April 10, 2018

Elisabeth A. Shumaker 

Clerk of Court
2 

This appeal involves issues of causation and exclusion of expert 

testimony. These issues arose in a suit by Ms. Samantha Hall against 

Conoco Inc., ConocoPhillips Company, and Phillips 66 Company 

(collectively, “ConocoPhillips”) on theories of negligence, negligence per 

se, and strict liability. 

Ms. Hall was diagnosed with leukemia, and she attributes the disease 

to a ConocoPhillips refinery’s emissions of a chemical known as benzene. 

Liability turned largely on whether benzene emissions had caused Ms. 

Hall’s leukemia. On the issue of causation, the district court excluded 

testimony from two of Ms. Hall’s experts and granted summary judgment 

to ConocoPhillips. We affirm because 

 the district court did not abuse its discretion in excluding the 

expert testimony and 

 expert testimony was necessary to create a genuine issue of 

material fact on causation because of the length of time 

between the exposure to benzene and the onset of Ms. Hall’s 

disease. 

I. Background

 As a child, Ms. Hall had lived near ConocoPhillips’s refinery in 

Ponca City, Oklahoma. Roughly two decades later, Ms. Hall developed a 

form of leukemia known as “Acute Myeloid Leukemia with Inversion 16.” 

This disease, according to Ms. Hall, resulted from her early exposure to the 

refinery’s emissions of benzene. 
3 

 In district court, Ms. Hall tried to prove this link through three 

expert witnesses: 

1. Dr. David Mitchell, an air modeler, 

2. Dr. Steven Gore, an oncologist, and 

3. Dr. Mary Calvey, an epidemiologist. 

Dr. Mitchell created an air model to estimate benzene concentrations near 

where Ms. Hall had lived. Based on Dr. Mitchell’s estimates, Dr. Gore 

 calculated Ms. Hall’s cumulative exposure to benzene and 

 used this calculation to opine that benzene exposure had caused 

Ms. Hall’s leukemia. 

Dr. Calvey expressed a similar opinion. 

 ConocoPhillips moved for 

 exclusion of opinion testimony by multiple expert witnesses, 

including Dr. Gore and Dr. Calvey and 

 summary judgment on the issue of causation. 

The district court granted the motion to exclude the expert testimony by 

Drs. Gore and Calvey. In the absence of their testimony, the court also 

granted summary judgment to ConocoPhillips, concluding that Ms. Hall 

had not presented sufficient evidence linking her disease to benzene 

exposure. 

II. Exclusion of Expert Testimony

 Ms. Hall challenges the district court’s exclusion of expert testimony 

by Drs. Gore and Calvey. We reject this challenge. 
4 

A. Standard of Review 

The district court has “wide latitude” in deciding whether to exclude 

expert testimony, and we review the manner in which the district court 

exercises this gatekeeping function for an abuse of discretion. Bitler v. 

A.O. Smith Corp., 400 F.3d 1227, 1232 (10th Cir. 2005). 

The district court’s exclusion of expert testimony is governed by 

federal law. See Sims v. Great Am. Life Ins., 469 F.3d 870, 879 (10th Cir. 

2006). Under Federal Rule of Evidence 702, a qualified expert witness may 

give opinion testimony if 

 the expert’s scientific knowledge would help the fact-finder 

understand the evidence, 

 “the testimony is based on sufficient facts or data,” 

 “the testimony is the product of reliable principles and 

methods,” and 

 “the expert has reliably applied the principles and methods to 

the facts of the case.” 

Fed. R. Evid. 702. 

 Before expert testimony can be admitted, the district court must 

determine that the proposed testimony is reliable. Daubert v. Merrell Dow 

Pharm., 509 U.S. 579, 589 (1993). The district court’s assessment of 

reliability is reviewed for an abuse of discretion. Goebel v. Denver & Rio 

Grande W. Ry., 346 F.3d 987, 990 (10th Cir. 2003). This review includes 

consideration of whether “the reasoning and methodology underlying the 
5 

expert’s opinion . . . is both scientifically valid and applicable to a 

particular set of facts.” Id. at 991. 

B. Dr. Gore’s Testimony

 Dr. Gore rendered a differential diagnosis on the cause of Ms. Hall’s 

leukemia. A differential diagnosis “rule[s] in all scientifically plausible 

causes of the injury and then rule[s] out the least plausible causes until 

only the most likely cause remain[s].” Id. at 990. 

 Dr. Gore’s first step was to rule in benzene, smoking, and idiopathic 

causes as potential causes of Ms. Hall’s leukemia.1

 Dr. Gore then ruled out 

smoking as a potential cause, leading him to conclude that benzene 

exposure had caused Ms. Hall’s leukemia. Dr. Gore did not expressly rule 

out the possibility of idiopathic causes. 

The district court assumed that a differential diagnosis could provide 

a suitable methodology. But the district court regarded Dr. Gore’s 

differential diagnosis as unreliable based partly on his failure to justify 

ruling in benzene or ruling out “idiopathic causes” of Ms. Hall’s disease. 

Hall v. ConocoPhillips, 248 F. Supp. 3d 1177, 1190-91 (W.D. Okla. 2017) 

(quoting Chapman v. Procter & Gamble Distrib., 766 F.3d 1296, 1311 

(11th Cir. 2014)). This reasoning fell within the district court’s discretion. 

 

1

 Dr. Gore and other experts explained that an “idiopathic” disease is a 

disease in which the cause is unknown. 
6 

1. Ruling In Benzene 

To use a differential diagnosis, Dr. Gore needed to consider whether 

he could rule in benzene as a potential cause of Ms. Hall’s disease. We 

may assume, as the district court did, that benzene emissions can cause 

Acute Myeloid Leukemia with Inverse 16. With this assumption, however, 

Ms. Hall would still have needed to show that the benzene emissions 

actually caused her disease. For this showing, Ms. Hall relied on Dr. 

Gore’s quantification of the exposure to benzene. 

To quantify the exposure, Dr. Gore used the work of another expert 

witness, Dr. Mitchell, who had constructed an air model to estimate the 

highest hourly average concentration of benzene. With this estimate, Dr. 

Gore quantified the cumulative exposure to benzene based on how long Ms. 

Hall had lived near the refinery.2

 The result led Dr. Gore to rule in benzene 

as a potential cause of Ms. Hall’s leukemia. 

The district court found two flaws in this methodology: 

1. Dr. Gore could not reliably use the highest hourly averageemission level to calculate Ms. Hall’s cumulative exposure to 

benzene. 

 

2

 Dr. Gore later upped his estimate of Ms. Hall’s total exposure based 

on new air modeling by Dr. Mitchell, which in turn had been based on new 

information. The supplemental estimates of Drs. Mitchell and Gore were 

excluded in district court based on a failure to timely disclose these 

estimates. The parties dispute the correctness of this ruling, but we need 

not reach the issue because we affirm the exclusion of Dr. Gore’s opinion 

based on flaws in his methodology. The newly acquired information did not 

affect these flaws.
7 

2. Dr. Gore’s calculation was based on mistakes involving the 

extent of Ms. Hall’s exposure to benzene. 

In finding these flaws, the district court acted within its discretion. 

a. The Choice of the Highest Hourly Average-Emission Level

 Dr. Gore estimated Ms. Hall’s cumulative exposure by taking one of 

Dr. Mitchell’s figures (the highest hourly average-emission level). 

ConocoPhillips questions the use of this figure, pointing out that Dr. Gore 

could have used other figures from Dr. Mitchell’s air model. 

 In this model, Dr. Mitchell had estimated benzene emissions over an 

extended time period. This estimate included the highest hourly average 

concentration of benzene while Ms. Hall lived near the refinery. Dr. 

Mitchell took this figure and instructed Dr. Gore to use it for his own 

calculation. 

But Dr. Mitchell admitted that he was not qualified to decide which 

figure to use in assessing the impact of benzene emissions on human 

health: 

Q. You are not qualified when it comes to analyzing what 

value—acute, chronic, subchronic—is more relevant for 

assessing human health risk for benzene or any other 

chemical. You are not qualified to offer that opinion. 

A. I fully agree with that. I’m an air modeler and I’m a 

meteorologist. 

 . . . 
8 

Q. And you don’t know which one of those matters most or 

matters at all for assessing whether or not Samantha Hall 

developed [acute myeloid leukemia] from benzene? 

A. Counselor, that’s out of my expertise. I’m not—I’m an air 

modeler and a meteorologist. 

Appellant’s App’x at 4944-45. Dr. Mitchell conceded that selection of the 

concentration level was best left to an oncologist like Dr. Gore.3

 In turn, 

Dr. Gore acknowledged that he had not independently chosen which figure 

to use. Instead, he had admittedly relied on Dr. Mitchell’s expertise to 

select the pertinent figure. 

Dr. Gore testified that he had called Dr. Mitchell, who provided 

assurance that the highest hourly average-emission level was the metric 

used in the industry. Appellant’s App’x at 5162. The district court could 

reasonably consider this assurance an inadequate safeguard of reliability. 

See Mitchell v. Gencorp Inc., 165 F.3d 778, 781 (10th Cir. 1999) (“The 

expert’s assurance that the methodology and supporting data is reliable 

will not suffice.”). 

 Without an adequate safeguard of reliability, the district court could 

reasonably conclude that neither Dr. Gore nor Dr. Mitchell could defend 

the use of the highest hourly average-emission level. Both expert witnesses 

 

3

 Dr. Mitchell noted that he was confident in his choice of the highest 

hourly average because this was the figure that other expert witnesses had 

always requested. But requests from other expert witnesses do not obviate 

the need for someone with expertise to select the appropriate concentration 

level for Dr. Gore’s calculation. 
9 

had seemingly disclaimed any responsibility for picking this figure: Dr. 

Mitchell had regarded Dr. Gore as the expert and Dr. Gore had regarded 

Dr. Mitchell as the expert, leaving no one qualified to choose which 

concentration level to use. 

This circular loop stirred broader concern over the entirety of Dr. 

Gore’s calculation. That calculation was designed to estimate Ms. Hall’s 

cumulative exposure to benzene. If Dr. Gore had calculated the cumulative 

exposure based on an incorrect figure, the court could reasonably question 

the decision to rule in benzene as a potential cause.4

 As a result, we 

conclude that the district court acted within its discretion in questioning 

the reliability of Dr. Gore’s decision to use the highest hourly averageemission level.

b. Dr. Gore’s Errors and Inconsistencies Regarding the Extent 

of Ms. Hall’s Exposure to Benzene 

 The district court also identified three of Dr. Gore’s errors and 

inconsistencies about the extent of Ms. Hall’s exposure to benzene. 

First, Dr. Gore assumed that Ms. Hall had lived near the refinery for 

eight years. But Dr. Gore was mistaken; Ms. Hall had lived near the 

refinery for only about four years. As Dr. Gore acknowledged, this error 

 

4

 Ms. Hall argues that medical doctors can rely on expert air modelers. 

Ms. Hall is correct, and the district court never suggested otherwise. The 

problem was that no one had justified the selection of the figure that was 

used in calculating Ms. Hall’s cumulative exposure to benzene. 
10 

meant that his estimate of the cumulative exposure was roughly double 

what it should have been. 

 Second, Dr. Gore vacillated on his own methodology. He initially 

stated that he had calculated Ms. Hall’s exposure by 

 using the highest hourly average-emission level from Dr. 

Mitchell’s model and 

 assuming that Ms. Hall had been exposed to that level for one 

hour every day. 

But in a later declaration, Dr. Gore stated that he had assumed exposure for 

8 hours per day, 5 days per week, 50 weeks per year. At a hearing, Dr. 

Gore switched back, testifying that his declaration had been mistaken and 

that he had actually assumed only one hour of exposure per day.

 Third, the district court found that Dr. Gore had been inconsistent 

about what he was calculating. He sometimes said that he was calculating 

Ms. Hall’s exposure to benzene; other times, however, he stated that he 

was calculating exposure to volatile organic compounds. These 

inconsistencies mattered because benzene is only one of many volatile 

organic compounds.5

 

5

 In his deposition, Dr. Gore estimated Ms. Hall’s exposure to benzene 

as only 20% of her broader exposure to volatile organic compounds. But 

Dr. Gore later backtracked, stating that his initial calculation had been 

solely for benzene and had excluded other volatile organic compounds. 
11 

In light of these errors and inconsistencies, the district court could 

reasonably question the reliability of Dr. Gore’s opinion ruling in benzene 

exposure as a potential cause. 

2. Ruling Out Idiopathic Causes 

Even if benzene could be ruled in as a potential cause, Dr. Gore’s 

differential diagnosis would have depended on his ability to rule out less 

plausible causes of Ms. Hall’s disease. The district court concluded that 

Dr. Gore had failed to rule out idiopathic causes, and this conclusion fell 

within the district court’s discretion. 

The parties agreed that acute myeloid leukemia is frequently caused 

by idiopathic sources. For example, Ms. Hall presented expert testimony 

that 70-75% of cases of acute myeloid leukemia are idiopathic. And Dr. 

Gore agreed that acute myeloid leukemia is ordinarily idiopathic in origin. 

The resulting question is whether Dr. Gore needed to consider and rule out 

idiopathic causes. The district court answered “yes.” 

A differential diagnosis is designed to identify the most likely cause 

of a disease. See Goebel v. Denver & Rio Grande W. Ry., 346 F.3d 987, 

990-91 (10th Cir. 2003). An expert need not consider and rule out every 

conceivable cause. See Bitler v. A.O. Smith Corp., 400 F.3d 1227, 1238 n.6 

(10th Cir. 2005); accord Best v. Lowe’s Home Ctrs., 563 F.3d 171, 181 

(6th Cir. 2009) (“[D]octors need not rule out every conceivable cause in 

order for their differential-diagnosis-based opinions to be admissible.”). 
12 

But the expert must still consider all plausible causes and rule out the less 

plausible ones until only the most likely cause remains. See Glastetter v. 

Novartis Pharm., 252 F.3d 986, 989 (8th Cir. 2001); see also Hollander v. 

Sandoz Pharm., 289 F.3d 1193, 1211-12 (10th Cir. 2002) (noting that a 

reliable differential diagnosis eliminates “all other possible causes of the 

victims’ condition . . . leaving only the toxic substance as the cause” 

(quoting Turner v. Iowa Fire Equip., 229 F.3d 1202, 1209 (8th Cir. 

2000))). 

Dr. Gore did not rule out the possibility of an idiopathic cause for 

Ms. Hall’s acute myeloid leukemia. This omission concerned the district 

court because the evidence had pointed to idiopathic causes in most cases 

of acute myeloid leukemia, and the district court could reasonably view the 

failure to rule out idiopathic causes as a fatal error tainting the differential 

diagnosis. See Milward v. Rust-Oleum Corp., 820 F.3d 469, 476 (1st Cir. 

2016) (upholding exclusion of expert testimony based on a differential 

diagnosis, reasoning that it was unreliable to link benzene to acute 

promyelocytic leukemia in part because the disease has an extraordinary 

number of idiopathic cases); see also Chapman v. Procter & Gamble 

Distrib., 766 F.3d 1296, 1311 (11th Cir. 2014) (holding that a failure to 

consider idiopathic causes rendered the differential diagnosis unreliable); 

Tamraz v. Lincoln Elec., 620 F.3d 665, 675 (6th Cir. 2010) (holding that 

expert testimony regarding causation of a given disease was inadmissible 
13 

because “the vast majority of . . . cases” involve “unknown (idiopathic) 

causation,” “making it impossible to ignore and rule out”); accord

Blanchard v. Goodyear Tire & Rubber Co., 30 A.3d 1271, 1275-76 (Vt. 

2011) (stating that the presence of a known risk factor is not sufficient to 

rule out idiopathic origin, particularly when most incidents of the disease 

lacked a known cause). 

 Ms. Hall responds with two arguments: 

1. The district court misunderstood the concept of “idiopathic” 

causes. 

2. The Tenth Circuit does not require differential diagnoses to 

rule out idiopathic causes. 

We reject both arguments. 

First, Ms. Hall argues that the district court misunderstood the term 

“idiopathic.” She characterizes “idiopathic” as a diagnosis by exclusion: 

only if all known factors are ruled out, leaving no known plausible factors, 

can the leukemia be considered idiopathic. Under this view, it is illogical 

to ask Dr. Gore to “rule out” idiopathic causes because a disease can be 

considered idiopathic only if all identifiable causes have been ruled out. 

Based on this definition of “idiopathic,” Ms. Hall regards the district 

court’s reasoning as faulty. To Ms. Hall, Dr. Gore properly ruled in all 

known risk factors and ruled out the implausible ones until he was left only 

with benzene. Because benzene remained a plausible cause, the term 

“idiopathic” would not fit. 
14 

But the district court could reasonably take a different approach 

when analyzing “idiopathic” causes. One can regard “idiopathic” causes as 

recognition of the medical community’s inability to identify all of the 

causes of a disease. See Tamraz v. Lincoln Elec., 620 F.3d 665, 668 (6th 

Cir. 2010) (stating that the term “idiopathic” is “another way of saying the 

medical community does not know why a given individual has the 

disease”); Huss v. Gayden, 571 F.3d 442, 459 (5th Cir. 2009) (indicating 

that a condition is “idiopathic” when “the medical community has a poor 

understanding of what causes it”); see also Vacuum Depositing, Inc. v. 

Dever, 285 S.W.3d 730, 733 (Ky. 2009) (“In common parlance, the term 

‘idiopathic’ means ‘arising spontaneously or from an obscure or unknown 

cause.’” (footnote omitted)). 

Because idiopathy accounts for more than half of the cases of acute 

myeloid leukemia, a differential diagnosis could be considered inherently 

unreliable here. See Tamraz, 620 F.3d at 675 (“[U]nknown (idiopathic) 

causation . . . currently accounts for the vast majority of Parkinson’s 

Disease cases, making it impossible to ignore and difficult to rule out.”); 

Bland v. Verizon Wireless, (VAW), 538 F.3d 893, 897 (8th Cir. 2008) 

(“Where the cause of the condition is unknown in the majority of cases, 

[the expert witness] cannot properly conclude, based upon a differential 

diagnosis, [the plaintiff’s] exposure to freon was ‘the most probable cause’ 

of [the plaintiff’s] exercise-induced asthma.”); see also Restatement 
15 

(Third) of Torts: Liab. for Physical and Emotional Harm § 28 cmt. c(4) 

(Am. Law. Inst. 2010) (“When the causes of a disease are largely unknown, 

. . . [a differential diagnosis] is of little assistance.”). Given the 

predominance of idiopathic causes, we conclude that the district court had 

the discretion to consider Dr. Gore’s differential diagnosis unreliable. 

Second, Ms. Hall contends that the Tenth Circuit does not require 

experts to rule out idiopathic causes in conducting a differential diagnosis. 

For this contention, Ms. Hall relies on Bitler v. A.O. Smith Corp., 400 F.3d 

1227 (10th Cir. 2005). Ms. Hall has misinterpreted Bitler. There we 

observed that an expert need not “‘categorically exclude each and every 

possible alternative cause.’” Bitler, 400 F.3d at 1238 n.6 (quoting Stephen 

A. Saltzburg et al., Federal Rules of Evidence Manual 702-33 (8th ed. 

2002)). This observation does not preclude a district court from 

questioning the reliability of a differential diagnosis when the cause of a 

disease is unknown most of the time. 

* * * 

 The district court could justifiably regard Dr. Gore’s differential 

diagnosis as unreliable because of his failure to (1) justify ruling in 

benzene or (2) rule out idiopathic causes. Thus, the district court did not 

abuse its discretion in excluding Dr. Gore’s opinion based on his 

differential diagnosis. 
16 

C. Dr. Calvey’s Testimony

 The district court also excluded Dr. Calvey’s opinion testimony 

linking benzene to Ms. Hall’s disease. Like Dr. Gore, Dr. Calvey 

conducted a differential diagnosis and opined that benzene had caused Ms. 

Hall’s leukemia. This opinion was excluded in part because Dr. Calvey had 

not “adequately address[ed] the issue of exposure.” Hall v. ConocoPhillips, 

248 F. Supp. 3d 1177, 1193 (W.D. Okla. 2017). Ms. Hall does not 

challenge this rationale, foreclosing reversal of the exclusion of Dr. 

Calvey’s testimony. See Bones v. Honeywell Int’l, 366 F.3d 869, 877 (10th 

Cir. 2004) (affirming a grant of summary judgment because the appellant 

failed to appeal an alternative basis for the ruling). 

III. Summary Judgment

Ms. Hall challenges not only the exclusion of expert testimony but 

also the grant of summary judgment to ConocoPhillips. The district court 

concluded that without the expert testimony by Dr. Gore and Dr. Calvey, 

Ms. Hall lacked the required evidence linking her disease to benzene 

emissions. Ms. Hall challenges this conclusion, arguing that the 

circumstantial evidence was enough to avoid summary judgment.6

 

6

 Both parties focus on Oklahoma law. Although federal law governs 

whether Ms. Hall presented sufficient evidence of causation to defeat 

summary judgment, state law governs “what theories of causation are 

permissible and the general means permitted to establish causation.” 

Tingey v. Radionics, 193 F. App’x 747, 760 (10th Cir. 2006) 
17 

We engage in de novo review of the grant of summary judgment. 

United States v. Turley, 878 F.3d 953, 956 (10th Cir. 2017). Summary 

judgment is appropriate only if the movant has shown 

 the absence of a genuine issue of material fact and 

 the movant’s entitlement to judgment as a matter of law. 

Gutteridge v. Oklahoma, 878 F.3d 1233, 1238 (10th Cir. 2018). 

For causation, Ms. Hall points to circumstantial evidence such as the 

presence of hydrocarbon leaks and odors in her neighborhood, groundwater 

contamination, a high benzene reading near her residence, and estimates by 

the Environmental Protection Agency showing increased risk from the 

refinery. This circumstantial evidence fails to create a genuine issue of 

material fact on causation because of the need for 

 expert testimony on the link between her disease and benzene 

exposure and 

 quantification of Ms. Hall’s exposure to benzene. 

A. The Necessity of Expert Testimony 

Ms. Hall’s circumstantial evidence does not create a genuine issue of 

material fact on causation because of the length of time between her 

exposure to benzene emissions and the onset of her disease. 

 

(unpublished); see Wackman v. Rubsamen, 602 F.3d 391, 400 (5th Cir. 

2010). The resolution of Ms. Hall’s claim depends on whether the type of 

evidence submitted constituted a permissible means of proving causation. 

Thus, we apply state law. See Tingey, 193 F. App’x at 760, 764; Wackman, 

602 F.3d at 400 & n.2. 
18 

Oklahoma law generally requires expert testimony for complex issues 

of medical causation. See, e.g., Christian v. Gray, 65 P.3d 591, 601-02 

(Okla. 2003) (“When an injury is of a nature requiring a skilled and 

professional person to determine cause and the extent thereof, the 

scientific question presented must necessarily be determined by testimony 

of skilled and professional persons.”); Ruland v. Zenith Constr., 283 P.2d 

540, 541 (Okla. 1955) (noting that the cause of an illness “is a matter of 

medical science to be established by expert testimony”). 

An exception exists “where the common knowledge or experience of 

laymen is extensive enough to recognize or infer negligence from the facts 

. . . with reasonable certainty.” Boxberger v. Martin, 552 P.2d 370, 373 

(Okla. 1976). But the district court could reasonably conclude that the 

long-term carcinogenic effects of benzene exposure lie outside the ken of 

common experience, requiring expert testimony. See Jones v. Ortho Pharm. 

Corp., 163 Cal. App. 396, 403 (1985) (stating that the etiology of cancer 

lies “beyond the experience of laymen and can only be explained through 

expert testimony”). 

In light of the need for expert testimony on the effects of benzene 

exposure, Ms. Hall could not avoid summary judgment by relying solely on 

circumstantial evidence linking her disease to benzene emissions. 
19 

B. Quantification of Exposure to Benzene

 When causation involves a link between a disease and exposure to a 

toxin, the exposure must ordinarily be quantified. See Mitchell v. Gencorp, 

Inc., 165 F.3d 778, 781 (10th Cir. 1999) (“‘Scientific knowledge of the 

harmful level of exposure to a chemical plus knowledge that plaintiff was 

exposed to such quantities are minimal facts necessary to sustain the 

plaintiff’s burden in a toxic court case.’” (quoting Allen v. Pa. Eng’g, 102 

F.3d 194, 199 (5th Cir. 1996))). Thus, Ms. Hall’s theory required not only 

expert testimony but also quantification of her exposure to benzene. See 

Twyman v. GHK Corp., 93 P.3d 51, 59-60 (Okla. Civ. App. 2004) (faulting 

an expert for his inability to identify the presence of a chemical at 

sufficient levels to have caused the injury). 

 Ms. Hall disputes the need to quantify her exposure. For this 

argument, Ms. Hall relies on Christian v. Gray, 65 P.3d 591 (Okla. 2003). 

There the plaintiffs asserted that they had become sick from inhaling 

airborne chemicals at a circus. Id. at 594. The Oklahoma Supreme Court 

concluded that the plaintiffs had not needed to quantify their exposure to 

the airborne chemical, reasoning that 

 this approach would “prevent many lawsuits based upon a 

single-event exposure, such as, for example, when a plaintiff 

brings an action and testifies of being enveloped by a great 

cloud of noxious gas from a calamitous event” and 

 “‘evidence of instantaneous onset of injury following a certain 

occurrence and expert testimony that the injury could have 
20 

been caused by the occurrence’” is enough to survive summary 

judgment. 

Id. at 606 (quoting Martin v. Stratton, 515 P.2d 1366, 1371 (Okla. 1973)). 

 In Christian, the court concluded that quantitative measurement is 

sometimes unnecessary when the plaintiff is exposed to an excessive 

amount of a chemical, followed quickly by the onset of symptoms. See id.

Our case is far different. Ms. Hall alleges long-term exposure to benzene, 

causing leukemia decades later. Thus, the Christian exception has no 

bearing here. 

* * * 

 To avoid summary judgment on the issue of causation, Ms. Hall 

needed both expert testimony and quantification of her exposure to 

benzene. Without the proposed testimony by Dr. Gore and Dr. Calvey, Ms. 

Hall lacked both the required expert testimony and a way to quantify her 

exposure to benzene emissions. Accordingly, the district court did not err 

in granting summary judgment to ConocoPhillips on causation. 

IV. Conclusion 

We conclude that the district court did not err 

 in excluding the testimony of Drs. Gore and Calvey and 

 in concluding that ConocoPhillips was entitled to summary 

judgment on causation. 

Therefore, we affirm.