Response to Comments Document concerning the proposed use of 

ASTM D6550-05 as an alternative test method for olefin content of gasoline

On July 6, 2006, the American Petroleum Institute (API) petitioned the Agency to allow 

ASTM D6550 as an alternative test method for measuring the olefin content of gasoline.1 The 

Agency agreed with this request, viewed API’s petition as non-controversial, and anticipated no 

adverse comments with API’s petition. On December 8, 2008, the Agency proposed, with a 

corresponding direct final rule, to allow the use of ASTM D6550-05 as an alternative test 

method for olefin content in gasoline provided: 1) ASTM D6550-05 results were correlated to 

the designated test method, ASTM D1319-03ε1, and 2) users of ASTM D6550-05 make use of the 

following conversion equation, Volume% = 0.857 X Mass%2, to convert mass percent olefins to 

volume percent olefins. In January, 2009, the Agency received an adverse comment from the 

New York State Department of Environmental Conservation (NYSDEC or DEC).3 On February, 6, 2009, 

the Agency published a partial withdrawal notice4of the direct final rule published on 

December 8, 2008, due to adverse comments submitted by NYSDEC.

The following is a brief summary of the NYSDEC adverse comments and API’s responses 

to them. 

Comments:

 

1

See Air Docket # EPA-HQ-OAR-2008-0558-0002.

2 This conversion equation was validated in ASTM D6550 for up to 10.5 weight percent olefins maximum in 

California gasoline meeting California Air Resource Board Phase 2 gasoline specifications.

3

See Air Docket# EPA-HQ-OAR-2008-0558-0005.

4

74 FR 6233, February 6, 2009.
2

NYSDEC argued that the use of ASTM D6550-05 would have the potential for producing 

results that are different from those produced with ASTM D1319-03ε1, and therefore, that test

results would not be consistent with EPA’s Complex Model. According to NYSDEC, a substantial 

volume of commercial gasoline has olefin content greater than 10.5 weight percent maximum 

for the proposed mass-to-volume conversion factor. Further, NYSDEC argued that the EPA 

proposed mass percent to volume percent conversion factor was not intended for universal 

use, that the use of this conversion factor as proposed on December 8, 2008, may not be 

appropriate for all gasoline, and would therefore, have the potential to underestimate olefin 

content when above 10.5 weight percent. 

On February 9, 2009, the American Petroleum Institute (API) responded to NYSDEC’s

comment and asked the Agency to promulgate a rule that would allow ASTM D6550-05 as an 

alternative test method for olefins in gasoline. This time, API requested the alternative test 

method, ASTM D6550-05, be correlated to the designated test method, ASTM D1319-03ε1, but 

without the use of the mass percent to volume percent conversion equation5 as earlier 

proposed.

API stated that a test facility that chooses to use any EPA-allowed alternative test 

method must first develop a site-specific correlation of the allowed alternative test method to 

the EPA-designated test method. According to API, in the case of an olefin content site-specific 

 

5

See Air Docket# EPA-HQ-OAR-2008-0558-0007.
3

correlation, the gasoline fuel set would span the olefin content range present and 

representative of the refinery or importer’s production. This gasoline fuel set would be 

analyzed by the test facility using both ASTM D1319-03ε1 and ASTM D6550-05. A correlation 

equation would then be developed from the results of both of these test methods in terms of 

ASTM D1319-03ε1 in volume percent versus ASTM D6550-05 in weight percent. Therefore, the 

applicable range of the resulting correlation from a site-specific correlation would be consistent 

with the specific refinery’s olefin content range. 

API also stated that if a test facility chooses to use an EPA-allowed alternative test 

method for analysis of a batch of gasoline, the laboratory would use the site-specific correlation 

equation as discussed previously to determine the designated test method value as if the 

gasoline sample had been analyzed by the EPA-designated test. In the case of the proposed 

ASTM D6550-05 alternative test method, it would be the ASTM D1319-03ε1 determined olefin 

value as derived from the site-specific correlation equation that is reported to EPA on batch 

reports and used as an input to the EPA Complex Model. According to API, the ASTM D6550-05 

result in weight percent would never be used directly for either compliance or as an input into 

the Complex Model for compliance demonstrations as described at 40 CFR Part 80. 

Finally, API argued that there would be no need to convert olefin content measured by 

ASTM D6550-05 in weight percent to volume percent because the olefin result as determined 

by ASTM D6550-05 would be correlated to the designated test method, ASTM D 1319-03ε1, 
4

based on a specific site’s gasoline production and, as previously stated, would never be used 

directly for either compliance or as an input to the Complex Model. Therefore, API 

recommended that EPA omit the initial conversion of ASTM D6550-05 weight percent to 

volume percent using the 0.857 factor and allow the use of ASTM D6550-05 as an alternative 

test method for olefin content in gasoline provided results are correlated to the EPA-designated 

test method, ASTM D1319-03ε1. 

On May 14, 2009, NYSDEC provided a response to API’s February 9, 2009 comments.

6

 

NYSDEC stated that the issue of the use of alternative test methods was discussed several times 

in the 1994 Reformulated Gasoline (RFG) Final Rule7. NYSDEC stated that in the 1994 RFG rule, 

“EPA saw two issues with alternative test methods – accuracy and bias. Therefore, in order to 

evaluate an alternative test method, accuracy and bias must be the primary considerations. 

We believe that the concerns voiced by EPA in 1994 regarding multiple regulatory test methods 

are still valid today.” NYSDEC also noted that most comments to the 1994 RFG final rule were 

in favor or ASTM D1319-88 as the designated test method for the measurement of olefin 

content in gasoline despite the method’s inability to accurately measure this property. They

also added concerns about the precision of the designated test method and added that little 

progress has been made in improving this method.

 

6

 See Air Docket# EPA-HQ-OAR-2008-0558-0008.

7

(59 FR 7716, February 16, 1994)
5

Further, NYSDEC reiterated its original comment that “[t]he Complex Model was built 

using fuels analyzed for their olefin content using the designated FIA method. Therefore, the 

important factor is how well values determined by an alternative test method compare to those 

determined in the past by the designated FIA (ASTM D1319) method. Whether or not the SFC 

method (D6550-05) is more accurate, precise, inexpensive or otherwise desirable over the FIA 

method should not be the primary issue for this rulemaking. To the extent that the SCF [sic]

method gives results which are different (without regard to being better or worse) from those 

of the FIA, the calculated results of the Complex Model will be different.” NYSDEC further 

stated that “[o]ur opposition to allowing ASTM D6550-05 as an alternative test method for 

ASTM D1319 is NOT based on a contention that ASTM D 1319 produced more accurate and 

precise estimations of the olefin content of gasoline. Our opposition is based on the fact that 

the algorithms used in EPA’s Complex Model were developed using olefin concentrations based 

solely on ASTM D1319. Therefore gasoline regulatory programs which are dependent on the 

Complex Model are also dependent on ASTM D1319.”(Emphasis in original).

NYSDEC also argued that API’s new approach to allowing ASTM D6550-05 as an 

alternative test method for measuring the olefin content of gasoline has little resemblance to 

that which was originally suggested in their July 6, 2006 letter. Further, NYSDEC stated that 

API’s new approach admits the 0.857 conversion factor for mass percent to volume percent is 

not appropriate. According to NYSDEC, API now “suggest[s] a site-specific correlation” of FIA 

volume percent data and SFC mass percent data, and that while this was an improvement on 
6

their original suggestion, it was insufficient evidence for EPA to entertain ASTM D6550-05 as a 

proposed alternative test method. 

NYSDEC also described the statement by API that “a laboratory that chooses to use any 

EPA-allowed alternative test method must first develop a site-specific correlation of the EPAallowed, alternative test method to the EPA-designated test method”, as largely meaningless. 

According to NYSDEC, “any two sets of data can be correlated. Correlation is only the process 

of examining data to determine if there is a linear relationship and to determine that strength 

of that relationship.” NYSDEC also stated that, “API presented no data to support its 

contention that “a linear relationship was found to exist between FIA and SFC over the zero to 

15 volume percent concentration range” and that the graphic is far too small to allow any 

analysis. NYSDEC also argued a lack of correlation because of API’s statement that “if needed, a 

nonlinear fit could easily be found to cover the zero to 20 volume percent range.” 

Finally, NYSDEC presented analysis of ASTM inter-laboratory crosscheck data, from 

January 2006 to October 2008, on measurement of olefins in gasoline that used ASTM D1319 

and ASTM D6550. According to NYSDEC, the analysis showed that although the square of the 

correlation coefficient was very good and the slope of the line was close to unity, the overall 

line was a poor fit for data on olefin concentrations of below 5 volume percent. NYSDEC also

presented an analysis of data for olefin concentrations of 10 to 24 volume percent that 

indicated the linear fit was poorer and noted that the slope of the least-squares linear-fit line 
7

was far from unity and the intercept very high. Finally, NYSDEC argued that while “calibration 

curves” of a single lab may appear better in terms of precision, there are no guarantees that 

any one lab would produce results that are more accurate than the average of a large number 

of labs subjected to statistical analysis.

On November 16, 2009, API provided a response8to NYSDEC’s May 14, 2009 letter. 

In regards to NYSDEC’s comment that there appears to have been little improvement in 

improving the FIA methods, API stated that the analytical instrument industry has given up 

attempts to improve the FIA method (ASTM D1319-03ε1) because the FIA method has 

fundamentally poor precision, and because a better method, SFC (ASTM D6550-05), has been 

developed.

In regards to NYSDEC’s comment that “whether or not the SFC method is more 

accurate, precise, inexpensive, or otherwise desirable over the FIA method should not be the 

primary issue for this rulemaking,” API responded that ASTM test methods are constantly being 

updated and improved to be more accurate and precise. Round robin test programs are 

routinely conducted to quantify improvements in the methods’ precision statements. Both 

industry and government labs participate in ASTM round robin programs, as well as the ASTM 

inter-laboratory crosscheck data programs with a goal of improving the accuracy and site 

precision of their particular labs. Also, a characteristic of world-class labs is that they use the 

 

8

See Air Docket# EPA-HQ-OAR-2008-0558-0009.
8

most up-to-date test methods having the best accuracy and precision. According to API, the 

purpose of EPA having allowed alternative test methods in the past has been to capture 

selected improvements in analytical technology and the concomitant improved operability, 

speed, accuracy, precision. Specific to olefin measurements, it is the uncertainty of the olefin 

measurements when using FIA that has led industry to develop the SFC method.

In regards to NYSDEC’s comment that, “to the extent that the SFC method gives results 

which are different from those of the FIA, the calculated results of the Complex Model will be 

different,” API responded that this statement indicated a misunderstanding of how the 

Complex Model is used in regulating fuels. According to API, this is because when an EPAallowed alternative test method is used, the alternative method result is translated into the 

“equivalent” result for the EPA-designated test method using the site-specific correlation 

required by EPA. It is the “equivalent” FIA result that is entered into the Complex Model, not 

the SFC result. “The test result from the alternative test method is never used directly for 

gasoline certification or for the Complex Model calculations. In addition, the test results using 

an alternative test method that has been well-correlated to FIA will be no more different from 

FIA that the difference between two repeat tests results obtained using FIA.” (Emphasis in 

original).

In regards to NYSDEC’s comment that their “opposition is based on the fact that the 

algorithms used in EPA’s Complex model were developed using olefin concentrations based 
9

solely on ASTM D1319. Therefore gasoline regulatory programs which are dependent on the 

Complex Model are also dependent on ASTM D1319,” API response was that “[i]f such logic 

were followed, progress would have stopped long ago. We would still be required today to use 

the version of each ASTM test method that was used to obtain the data for development of the 

Complex Model. For example, we would be required to use ASTM D323 for measuring gasoline 

vapor pressure, which was abandoned in 1991 when ASTM D5191 was adopted in 1992. Also, 

the ASTM standard specification for gasoline would be a very outdated D439 rather than 

today’s D4814. And, we’d be stuck with a 1990 vintage vehicle fleet for our driving needs 

because that is the technology that the Complex Model is based upon.”

In response to NYSDEC describing API’s statement that “[a] laboratory that chooses to 

use any EPA-allowed alternative test method must first develop a site-specific correlation of the 

EPA-allowed, alternative test method to the EPA-designated test method,” as “largely 

meaningless” API responded that “NYSDEC appears to be unaware that except for the diesel 

rule where EPA adopted a performance based approach in approving diesel sulfur test 

methods, EPA has required that any lab that wishes to use an EPA-allowed alternative test 

method must develop and maintain such a site-specific correlation. The correlation 

requirement for each of the nine alternative test methods currently allowed by EPA is not 

meaningless, but rather a federal EPA requirement.”
10

API responded to NYSDEC’s comment that “API presents no data to support the 

statement that a linear relationship was found to exist between FIA and SFC over the zero to 15 

volume percent concentration range” by stating that “Figure 1 in the July 6, 2006 API letter is 

reproduced below to demonstrate the linearity of the matter over the zero to 15 volume 

percent range. Note that the results in this plot include the use of the 0.857 factor only 

because we chose to reproduce the original plot shown in the July 6, 2006 letter. The use or 

omission of the conversion factor makes absolutely no difference in any conclusions regarding 

the linearity of the data.”

In regard to NYSDEC’s comment that “EPA’s lab would not be able to test fuels because 

correlations will be refinery-[specific] and laboratory-specific. Therefore, enforcement will be 

hindered as EPA would not be able to recreate the correlations used,” API stated that “EPA’s 

enforcement of its fuel standards is completely independent of the EPA-allowed alternative test 

methods being used by labs, as well as related site-specific correlations. Whereas EPA may use 

non-designated test methods for screening purposes on occasion, we understand that all EPA 

enforcement is based on measurements obtained using EPA-designated test methods.”

In regard to NYSDEC comment that they also have issues with how ASTM analyzes round 

robin program data and inter-lab crosscheck data using “robust statistics,” API responded that 

“the ASTM statistical package used to analyze the data has been peer reviewed and accepted 

by statisticians in industry and governments across the globe.” 
11

Further, API noted that NYSDEC’s May 14, 2009 letter, persistently referred to the API 

February 9, 2009 letter as a “new proposal.” As one example they cited NYSDEC’s statement 

that “API’s newly suggested method has little resemblance to that which they originally 

suggested in their July 6, 2006 letter. API’s new approach admits that the 0.857 conversion 

factor for mass percent to volume percent is not appropriate.” In response, API notes that their 

February 6, 2009 letter, recommended that the EPA regulation omit the initial conversion of the 

D6550 weight percent to its volume percent using the 0.857 factor. According to API, as 

explained in that letter, the use or omission of the conversion factor would make absolutely no 

difference in any reported olefin result in the proposed rule. Finally, API recommended again 

that EPA allow ASTM D6550-05 as an allowed alternative to the designated test method, ASTM 

D1319, for measuring olefin content of gasoline, provided the results are correlated with ASTM 

D1319 using a refinery-specific correlation of FIA (volume %) versus SFC (weight%).”

EPA Response to API & NYDEC comments:

In today’s action, EPA is proposing to allow ASTM D6550-05 (SFC) as an alternative to 

the designated test method, ASTM D1319-03ε1 (FIA), for measuring olefin content of gasoline, 

provided the results are correlated to ASTM D1319-03ε1 using a site-specific correlation of FIA 

(volume percent) versus SFC (weight percent). The Agency is also proposing that correlation be 
12

completed on a site-specific basis. The Agency believes it is in a test facility’s best interest to 

ensure that the gasoline fuel set used to develop the correlation spans the range of olefin 

properties representative of that refinery’s or importer’s gasoline production. This gasoline 

fuel set would be analyzed by the test facility’s laboratory using both ASTM D1319-03ε1 (also 

known as FIA, or the designated test method) and ASTM D6550-05. A resulting correlation 

equation would then be developed in terms of ASTM D1319-03ε1 in volume percent and ASTM 

D6550-05 in weight percent. Thus, the applicable range of the resulting correlation from a 

facility’s site specific correlation would be consistent with that specific facility’s olefin content 

range. Furthermore, the requirement of correlating SFC test methods results to the FIA 

designated test method produces an SFC-FIA equivalent result that is suitable for input into the 

Complex Model or for meeting fuel reporting requirements. 

The Agency agrees with API’s recommendation that there is no need to convert olefin 

content measured by ASTM D6550-05 in weight percent to volume percent because the olefin 

result as determined by SFC (ASTM D6550-05) is correlated to FIA (ASTM D1319-03ε1) based on 

a specific site’s production and never used directly for compliance or as an input into the 

Complex Model. Thus, in today’s proposal, EPA is omitting the initial conversion of olefin 

content measured by ASTM D6500-05 in weight percent to volume percent using the 0.857 

factor, as earlier proposed on December 8, 2008.
13

The Agency agrees with NYSDEC that a bias in gasoline olefin measurement results may 

exist between ASTM D1319-03ε1 and ASTM D6550-05. In order to compensate for any bias that 

may exist between these two analytical test methods, EPA is proposing to require ASTM D6550-

05 to be correlated to ASTM D1319-03ε1, its respective designated test method. Refiners or 

importers that choose to use ASTM D6550-05 for the measurement of olefin content in 

gasoline must report the correlated result, on a site-specific basis, with the designated method, 

ASTM D1319-03ε1, when using the proposed EPA-allowed alternative test method, ASTM 

D6550-05. 

The agency also notes that Figure 1 from API’s July 6, 2006 letter illustrates a confidence 

plot from ASTM standard practice ASTM D6708 for ASTM D6550 vs. ASTM D1319. The fuels 

samples used in the ASTM crosscheck program were provided to ASTM on a global basis, not 

from a specific refinery. The Agency believes that because the fuel samples provided to ASTM 

for their crosscheck program are provided to ASTM on a “global” basis, one would expect that 

these fuel samples would vary in olefin content more than if they were provided from a specific 

refinery. Thus, the ASTM D6708 confidence plot using ASTM crosscheck data represents a 

robust data set compared to if the same confidence plot were derived from a specific refinery. 

The Agency also believes that API’s intent in using this illustration was not to establish a 

“global” linear correlation between these two methods, but to show that a linear relationship 

could be established between these two methods using a robust fuels data set on olefin 

content from the ASTM crosscheck program. The Agency believes that this illustration of a 
14

linear relationship between SFC and FIA from the ASTM crosscheck program is sufficient 

evidence to illustrate that a linear relationship may be established between these two test 

methods. Moreover, if a linear relationship can be established between two analytical test 

methods with fuel samples representing producers on a “global” scale, then one would expect 

that a linear relationship may be established between these two test methods on a site specific 

basis, where olefin content variance in gasoline fuel samples would not be expected to be as 

varied, compared to fuel samples from an ASTM crosscheck program. 

The Agency does not believe that the adoption of alternative test methods for 

compliance measurements hinders its enforcement ability. Rather, the Agency believes that 

the adoption of alternative test methods used for compliance measurement provides flexibility 

to the regulated industry by allowing methods that may be less expensive, increase speed of 

analysis, or may be more accurate or precise. We also believe that our approval of this 

alternative test method would not be inconsistent with the Agency’s posture in the RFG rule. 

This is because, as discussed previously, the requirement of correlating EPA-allowed alternative 

test method results to its respective designated test method compensates for any bias that may 

exist between the alternative and designated test method. Additionally, as also previously 

discussed, the liner relationship would likely assure accuracy. Moreover, while the Agency may 

use non-designated test methods for enforcement screening purposes, it uses the designated 

test method specified in the regulations for each particular fuel parameter for purposes of 

enforcement.
15

Further, we believe today’s proposal is consistent with past Agency practice because the 

Agency currently allows eight alternative test methods for the measurement of gasoline or 

butane properties provided their results are correlated to the fuel parameter’s respective EPA 

designated test method. These alternative test methods are: ASTM D5453, ASTM D6920, ASTM 

D3120 and ASTM D7039 for sulfur in gasoline9, ASTM D4468 and ASTM D3246 for sulfur in 

butane10, ASTM D1319 for aromatics in gasoline11, and ASTM D4815 for oxygenate content of 

gasoline.12 In addition, ASTM D4294, ASTM D6920 and ASTM D5453 are approved alternative 

test methods for measuring the sulfur content of 500 ppm diesel fuel provided its test results 

are correlated to the designated test method, ASTM D2622.13

Finally, although not the subject of this proposed rulemaking, EPA intends to establish a 

performance-based test method approach (PBTM) rule which would provide criteria for the 

qualification of alternative test methods. 

 

9

See 40 CFR § 80.46(a)(3)(i) through § 80.46(a)(3)(iv).

10 See 40 CFR § 80.46(a)(4)(i) through § 80.46(a)(4)(ii).

11 See 40 CFR § 80.46(f)(3)(i).

12 See 40 CFR § 80.46(g)(2)(i).

13 See 40 CFR § 80.580(c)(2).