Rentech ( RTK) surged on news that the alternative-fuel company had entered an agreement with Peabody Energy ( BTU) to convert coal into diesel and jet fuel. Two projects will be located on Peabody reserves and will convert coal into clean transportation fuels using Rentech's proprietary process. Shares of Rentech jumped 93 cents, or 22.1%, to $5.13. Peabody Energy rose 71 cents, or 1.4%, to $50.90. GEO Group ( GGI) gained after the operator of correctional and detention centers increased its second-quarter guidance. GEO expects to earn 67 to 70 cents a share, excluding items, with revenue of $205 million to $210 million. The company had projected a profit, before items, of 55 cents to 58 cents, and revenue of $185 million to $190 million. GEO's full-year profit outlook was boosted to a range of $2.27 to $2.37 a share from $2.11 to $2.21, and its revenue prediction went to between $790 million and $805 million from $770 million to $785 million. Shares of GEO were higher by $4.54, or 13.7%, to $37.59. SimpleTech ( STEC) rose more than 14% following the company's announcement that its revenue and earnings for the second quarter should significantly exceed its previous guidance. The company currently expects revenue for the second quarter to range from $78 million to $79 million, with earnings of 9 cents to 10 cents a share. The prior forecasts were for a profit of 5 cents and revenue of $67 million to $70 million. SimpleTech, a developer of DRAM memory modules, flash drives and memory cards, was up 55 cents to $4.40. Centene ( CNC) plummeted after the company dramatically lowered its profit forecast for this year, citing detrimental medical cost trends. For 2006, Centene is now expecting to earn 95 cents to $1.04 a share, down from its previous guidance of $1.53 to $1.70. That sent the stock reeling, and it was lately down $7.60, or 36.1%, to $13.44, making it the biggest percentage loser on the New York Stock Exchange. More than 20 times the normal volume of shares had been traded.