After his rugby career was ended by injury, Gammell followed his father into business. Using venture capital, he founded Cairn Energy in Edinburgh. The company invested in several unsuccessful oilfields in the United States before making a modest strike in the Pennsylvania oilfield. Gammell was appointed Cairn's Chief Executive on its initial listing in 1989. In the mid 1990s, he led the company in a radical reallocation of its assets, moving out of US and North Sea oil and gas concerns and into neglected fields in South Asia. The company's fortunes soared in 2004, when a field it had bought in 2001 (for $7.5 million) from Shell in the Indian province of Rajasthan was found to contain close to 1.1 billion barrels of oil, catapulting it into the FTSE 100.