BlackRock Inc. said on May 12 that it voted in favor of a successful shareholder proposal calling for more climate change reporting by Occidental Petroleum Corp., in the first sign the world's largest asset manager was backing up its tough new talk on environmental matters.

Backers of the resolution called its passage a major victory, the first time such a measure succeeded at a major U.S. oil and gas company. Proponents said they were pleased by BlackRock's support, which they had sought.

"Today’s historic vote puts the oil and gas industry on notice – the climate is changing and so are investor expectations of how companies should respond," said Laura Campos, a director at the Nathan Cummings Foundation, one of the resolution's proponents.

BlackRock, which has $5.4 trillion under management, traditionally has given few details of its reasoning behind specific proxy votes. On Friday, however, it said it was concerned about Occidental’s pace of disclosure to date. It also gave details about its talks with other companies such as Chevron Corp, which BlackRock said has provided more detail on climate risks it faces such as a recent report it published.

A Chevron representative said the company would continue speaking with investors, and that it had held “extensive dialogue with proponents and other stockholders."

BlackRock spokesman Ed Sweeney said BlackRock would not explain every vote it casts in such detail but wanted to underscore how it promotes its corporate governance priorities in talks with companies.