Qteros, a US-based developer of biofuels previously backed by oil groups BP and Valero Energy, is reportedly looking to raise a $40m funding round.
The series D round was reported by VentureWire, citing an executive at the company.
The company raised $22m in its series C round in January. No investors were disclosed in this round, although beyond the two oil groups, other previous investors have been venture capital firms Battery Ventures, Venrock, Soros Fund Management, Long River Ventures and Camros Capital.
Qteros, formerly known as SunEthanol, raised $25m in its series B round in November 2008.
The company raised a series A in 2007, and a regulatory filing for that year shows it filed to raise a $2.5m round. The various fundraisings suggest the company is looking to nearly double what it has raised so far, from $49.5m to $89.5m.