New York Attorney General Eric Schneiderman is investigating ExxonMobil Corp.'s (NYSE: XOM) accounting practices and why the company hasn't written down the value of its assets despite a steep drop in oil prices, the Wall Street Journal reported, citing people familiar with the matter.

A more than 60% plunge in oil prices since mid-2014 has forced oil producers worldwide to write down the value of their assets.

In a note earlier this month, Jefferies LLC estimated that a group of integrated oil companies had impaired assets worth $103 billion since the start of 2014. This is equivalent to 8% of their 2014 net assets.

The brokerage expects more asset impairments in the industry, noting that ExxonMobil is the only major producer to not have written down any assets.

ExxonMobil and the New York Attorney General's office were not immediately available for comments.

Schneiderman's office launched an investigation last year into whether ExxonMobil misled the public and shareholders about the risks of climate change.

RELATED: States Sign Pact To Keep ExxonMobil Climate Probe Confidential

Voters at ExxonMobil's annual meeting in May approved a measure to let minority shareholders nominate outsiders for seats on the board, meaning a climate activist could eventually become a director at the world's largest publicly traded oil company.

Exxon's shares were down about 1.5% at $83.80 premarket. Up to close Sept. 15, shares of the company had fallen about 17% since mid 2014, trailing a 32% decline in the broader S&P Energy index during the same period.