Gas contract whereas all the gas in a specific field is dedicated to a single buyer. A depletion contract is usually for smaller amounts of gas or oil and it refers to a contract to supply hydrocarbons to a buyer from a seller’s specific dedicated field (as opposed to supply contract). In a depletion contract the buyer contracts to purchase all the gas that can be economically produced from a particular reservoir before a specified termination date. In gas purchase contracts, a depletion contract is an agreement to purchase the output of a field over its whole lifetime