Occidental Petroleum is making a transformational transaction.Warren Buffett has long held Occidental Petroleum (OXY -7.16%) and its CEO, Vicki Hollub, in high regard. His trust in Hollub led Buffett's company to invest heavily in Occidental. Berkshire Hathaway (BRK.A -0.14%) (BRK.B -0.40%) now owns over $12.6 billion of Occidental's stock -- almost 27% of its outstanding shares -- making it Berkshire's sixth-largest holding at 4.1% of the investment portfolio. In addition to Occidental's leadership, Buffet ...