Exxon Mobil Corp. said Tuesday it will make its first major investment in greenhouse-gas reducing biofuels in a $600 million partnership with biotech company Synthetic Genomics Inc. to develop transportation fuels from algae. Despite record-breaking profits in recent years, the oil and gas giant has been criticized by environmental groups, members of Congress and even shareholders for not spending enough to explore alternative energy options. One of the company's requirements was finding a biofuel source that could be produced on a large scale. It says photosynthetic algae appears to be a viable, long-term candidate. If the alliance proves successful, pumping algae-based gasoline at Exxon service stations is still several years away and will mean additional, multibillion-dollar investments for mass production.