As of September 2015, BP last split its stock on Oct. 4, 1999, doubling its number of shares and halving their price, according to BP. Stockholders' existing share prices were cut in half, and they were issued one new share for each share they already owned.
BP chose to split its shares in 1999 to normalize its stock prices with those of similar companies in its sector for the purpose of competition, according to BP. The split did not change the valuation of the company but divided the value across more stock shares. The dividends BP pays its shareholders were split with the share prices.
The 1999 stock split followed an eight-year rally in stock price for BP, reports Yahoo! Finance. Shares in BP traded near $11 in October 1992 and had nearly sextupled to $59 by October 1999. BP's price per share fluctuated from late 1999 through the spring of 2002 before dropping in the first half of 2003. Shares in BP rose steadily from mid-2003 through 2005 and then maintained a price above $60 until mid-2008 when prices dropped. BP shares reached a 10-year low in 2010, plummeting below $29 per share. BP stock rose over the period from 2010 to 2015 before falling back to 2010 levels in the fall of 2015.