The energy-focused First Reserve, finishing investing from its first infrastructure fund, is beginning fundraising for a second fund targeted at roughly $1.25 billion,according to different sources.

The first fund raised $1.23 billion in 2009 and was focused on investing in power generation, regulated power transmission and distribution, and midstream oil and gas transmission assets. Since its launch, the fund invested in seven companies.

First Reserve paired up with SunEdison, the solar development arm of MEMC Electronic Materials Inc., to acquire solar projects and with the Madrid-based wind developer Renovalia Energy Inc. to buy its wind assets.

In the midstream oil and gas market First Reserve joined with publicly traded oil and gas company Triangle Petroleum Corp . to form Caliber Midstream Partners LP ; and worked with Energy Corporation of Americato form First ECA Midstream , which holds a gas-gathering system in the Marcellus Shale.

Other assets acquired by First Reserve's initial infrastructure fund include the Ft. Detrick power plant in Maryland; First Caribbean Power and Midstream, a platform to own contracted power and midstream assets in the Eastern Caribbean, and a similar company, North American Power, focused on acquiring contracted power assets in the U.S.