“That such an obvious problem could escape notice in this high-profile, landmark study highlights the need for increased vigilance in all aspects of quality assurance” for all methane measurement programs, he wrote.

The paper appears in the journal Energy Science & Engineering.

The Texas study, the first of 16 reports on methane emissions sponsored by the Environmental Defense Fund, measured emissions at 190 natural gas production sites.

The lead author of the Texas study, Prof. David T. Allen, stood by his work. “There may be issues with some of these instruments, but we tested our instruments pretty thoroughly and when we went out into the field we had multiple instruments, all of which gave us information,” he said. Alternate measurement methods were used at some sites, he said, and “we didn’t see any evidence that we were missing any large numbers.”

The maker of the instrument, Bacharach, reviewed Mr. Howard’s new paper, along with one he co-wrote earlier this year. It issued a statement that the sampler, first produced in 2003, was initially tested and validated with gas streams that are not the same as those in the study, which involved high levels of the class of chemicals known as volatile organic compounds.

Even so, the company stated, “we believe that some of the primary test results and conclusion” of the studies “are not valid” because the sensor failures reported by Mr. Howard could be caused by other factors. The company suggested frequent recalibration of the device, and said it would update operating manuals; it also recommended further testing.

A spokeswoman for the E.P.A. said the agency would assess information “from a number of channels,” including the research community and industry and the new Howard paper, “as a part of our routine review of new information” for its annual inventory of greenhouse gases.

Methane is the main component of natural gas, and the expansion of techniques such as hydraulic fracturing, known as fracking, has greatly increased the amount of natural gas being extracted, sold and transported around the country. This shift has been widely hailed as environmentally helpful, to the extent that more reliance on natural gas to generate electricity means less reliance on coal and thus smaller amounts of carbon dioxide and other pollutants being pumped into the atmosphere.