αs from the top quark pair production cross section

Five measurements of the top quark pair production cross section from hadron colliders are compared with the theoretical prediction (up the next-to-next-to-leading order in QCD) in order to determine the strong coupling constant αs. The determination is performed for several PDF sets. The individual determinations of αs are combined to form a single best estimate using the Best Linear Unbiased Estimate (BLUE) procedure. Preliminary combined results indicate a higher value of αs than that determined in a previous extraction of αs from the top quark pair production cross section.