Among the premarket stories for Tuesday, Dec. 23, from AP Financial News:

DETROIT (AP) - Shares of General Motors Corp. and Ford Motor Co. fell in premarket trading Tuesday after two debt rating companies lowered ratings on the automakers.

NEW YORK (AP) - Tibco Software Inc.'s better-than-expected fourth-quarter earnings are drawing mixed reviews from Wall Street analysts after the company's revenue declined.

NEW YORK (AP) - An analyst has cut his estimates on PPG Industries Inc., saying the chemicals maker likely will continue to be affected by a drop in demand from the automotive sector.

NEW YORK (AP) - The likelihood that Smurfit-Stone Container Corp. will be forced to restructure its balance sheet led an equity analyst Tuesday to downgrade shares of the containerboard maker.

NEW YORK (AP) - Red Hat Inc. shares rose in premarket trading Tuesday after the company posted better-than-expected third-quarter earnings.

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