Oil and Natural Gas Corp (ONGC), India's largest oil and gas producer, today supported demands for imposition of a windfall profit tax saying it was willing to forgo part of incremental revenues from high oil prices towards subsidising fuel. ONGC, which on an ad hoc basis is asked to meet part of revenue losses on sale of petrol, diesel, LPG and kerosene, wants a transparent system that may include raising cess on crude oil production and a new levy on prices above a certain level.