American Express may be making headway once again in the credit card market through its "companion" card alliances with several banks.Monthly data on payment card use from the Reserve Bank of Australia shows that the combined market share of American Express and Diners Club lifted to 16.4 per cent in December 2009, up from 15.8 per cent a month earlier and up from 14.4 per cent in December 2008.MWE Consulting in their monthly analysis of the RBA data noted that this was the third consecutive month in which the three party card schemes (Amex and Diners) gained share from the "four party" schemes (MasterCard and Visa). The MasterCard and Visa market share, worked out on an annual basis, dipped to 84.9 per cent.MWE conclude that the increasing number of three party companion cards is making an impact. There is some evidence for that in the rising market share of credit card balance of two banks that have promoted Amex companion cards this year.Commonwealth Bank in particular has aggressively promoted the Amex companion card in recent months. CBA accounted for one third of all the growth in consumer card balances in the December 2009 quarter. CBA and ANZ together accounted for half of all the growth.