The vanadium containing heteropolyacids H-4[PMo(11)VO40] x 34H(2)O (HPA-1), H-5[PMo10V2O40] x 32H(2)O (HPA-2) and H-6[PMo9V3O40] x 34H(2)O (HPA-3) act as highly active catalysts for the direct transformation of light C-1-C-3 alkanes into the corresponding carboxylic acids in the presence of CO and in the K2S2O8/CF3COOH system. Propionic acid (ca. 70% yield), iso- and n-butyric acids (ca. 65% overall yield), and acetic acid (ca. 20%) are the major products obtained from the carboxylation of ethane, propane and methane, respectively, with vanadium playing a main catalytic role. The effects of the catalyst amount have been studied and overall turnover numbers (TONs) up to ca. 12 x 10(3) (for the ethane and propane conversions) or up to 3 x 10(3) (for the methane carboxylation to acetic acid) have been achieved for very high alkane-to-catalyst molar ratios which also promote the selectivity towards acetic acid. (C) 2007 Elsevier B.V. All rights reserved.