Exxon Mobil Corp. for years has kept the value of its huge oil and gas reserves steady in the face of slumping energy prices while rivals since 2014 have slashed $200 billion off their combined holdings.

Analysts and investors have taken notice, and now a Wall Street antagonist, New York Attorney General Eric Schneiderman, is examining accounting practices at the nation’s largest energy company, according to people familiar with the matter. His office is adding scrutiny of its reserve values to its probe into Exxon’s past knowledge of the impact of climate change and how it could affect its future business.

The Irving, Texas-based company has played down questions about its lack of assets write-downs, saying it is extremely conservative in booking the value of new fields and wells. That reduces its need to reduce the value of its assets if falling prices later weigh on the reserves’ value, Exxon says.

Exxon declined to comment on the New York investigation, and wouldn’t disclose specifics of how it evaluates assets apart from what it has said in company filings. A spokesman said Exxon follows all financial rules and regulations.

PricewaterhouseCoopers LLP, Exxon’s auditor, declined to comment on the investigation.