This excerpt taken from the BP 6-K filed Mar 13, 2006.
Interests in associates - concluded
The results, assets and liabilities of an associate are incorporated in these financial statements using the equity method of accounting. Under the equity method, the investment in an associate is carried in the balance sheet at cost plus post-acquisition changes in the Groups share of net assets of the associate, less distributions received and less any impairment in value of the investment. The group income statement reflects the Groups share of the results after tax of the associate. The group statement of recognized income and expense reflects the Groups share of any income and expense recognized by the associate outside profit and loss.
The financial statements of associates are prepared for the same reporting year as the Group. Where necessary, adjustments are made to those financial statements to bring the accounting policies used into line with those of the Group.
Unrealized gains on transactions between the Group and its associates are eliminated to the extent of the Groups interest in the associates. Unrealized losses are also eliminated unless the transaction provides evidence of an impairment of the asset transferred.
The Group ceases to use the equity method of accounting on the date from which it no longer has significant influence in the associate or when the interest becomes held for sale.