Centrica and Drax have signed a five-year agreement that gives Centrica access to 300MW of extra baseload power.
The deal, which enables additional coal-indexed power volumes, will come into force from October 2010.
According to the agreement, Drax will provide power to Centrica at a price set in line with global coal prices and fixed clean dark spreads, while Centrica will deliver matching carbon allowances.
The agreement is in line with Centrica's strategy to ensure secure energy supplies for its customers and to diversify its fuel mix, further reducing its overall exposure to the gas price in the UK, the company said in a statement.
The agreement is similar to a 600MW supply contract, which came into effect in October 2007.