India has set the ceiling price for gas to be produced from difficult fields at $6.61 per MMBtu for the April-September period, a source with knowledge of the matter said on Thursday. The price will be applicable on gross heat value basis. The is the first time that the country has set a price for the cleaner fuel that has been discovered but not yet produced from deep-water, ultra deep-water and high-temperature and high-pressure fields. Last month, India unveiled a slew of reforms including gas pricing and marketing freedom to the contractors operating challenging fields, as the South Asian nation hoped to unlock resources worth almost $40 billion.