Prospect Medical agreed to be purchased by private-equity firm Leonard Green & Partners in a deal that values shares of the healthcare services provider at $8.50 a share, nearly a 40% premium to Friday's closing price. Shares of Prospect Medical jumped by $2.29, or 37.4%, to $8.41. Volume topped 785,000 shares, compared to the average daily share volume of 19,000. In other M&A news, Allis-Chalmers Energy ( ALY) continued to rally after SeaDrill's ( SDRL) Seawell unit agreed last week to acquire the company for $4.25 in cash or 1.15 shares of the subsidiary. Shares of Allis-Chalmers have jumped 80% over the last three trading sessions to $4.14. Volume topped 5.73 million shares, compared to the average daily share volume of 527,000. Superior Bancorp ( SUPR) slumped by 23 cents, or 14.8%, to $1.32 after the company posted a second-quarter net loss of $53.7 million, or $4.44 a share, compared with a loss of $5.74 million, or 49 cents a share, in the first quarter of 2010 and a loss of 68 cents a share in the year-ago quarter. Superior Bancorp said the second-quarter loss was driven by provision for loan losses of and losses on other real estate owned.. Volume topped 87,000 shares, compared to the average daily share volume of 28,000. BioFuel Energy ( BIOF) fell by 11 cents, or 8.2%, to $1.24 after the company said late Friday that it had a second-quarter loss of 37 cents a share, widening from a year-ago loss of 28 cents a share. Revenue fell 9% from a year ago to $96.4 million. Volume topped 187,000 shares, compared to the average daily share volume of 102,000. -- Written by Robert Holmes in Boston. Check out all of Monday's high-volume, under-$5 stocks at the Dollar Store. View the Dollar Store portfolio on StockPickr. Follow Robert Holmes on Twitter and become a fan of TheStreet.com on Facebook.