Despite its size, Berkshire had for many years not been included in broad stock market indices such as the S&P 500 due to the lack of liquidity in its shares; however, following a 50-to-1 split of Berkshire's Class B Shares in January 2010, and Berkshire's announcement that it would acquire the Burlington Northern Santa Fe Corporation, parent of BNSF Railway, Berkshire replaced BNSF in the S&P 500 on February 16, 2010.[17][18]