SAN FRANCISCO (MarketWatch) -- Sears Holdings Corp. SHLD+4.53% will be booted from the S&P 500 Index SPX+0.08% at the close of trading Sept. 4 and replaced by chemical and polymer maker LyondellBasell Industries NVLYB-0.40% , Standard & Poor's said late Wednesday. "Sears' public float has been well below the 50% threshold for inclusion for an extended period of time and is no longer considered representative of the index," S&P said in a statement. Private hedge fund ESL Investments Inc. and its manager Edward Lampert own a total of 65.7 million, or nearly 62%, of Sears' 106.4 million outstanding shares, according to FactSet. In a statement, Sears stressed that the action was a result of the public float level and not a valuation of the company's performance, noting that S&P had recently raised the retailer's credit rating outlook to stable from negative. Indeed, S&P on Aug. 17 raised the outlook while affirming its CCC+, or junk, rating on Sears. Shares of Sears fell 3.4% to $55.50 and LyondellBasell shares rose 4% to $49.20 in after-hours activity.