The active capacity of the world's 20 largest ocean container carriers shrunk by 2.4% over the past year, but there was relatively little change in their global market shares.

The top 20 lines actually boosted their combined fleets by 1.6% in the year to Jan. 1, 2010, but their effective capacity declined as they idled more vessels in response to lower cargo volume, according to Alphaliner, the Paris-based container shipping consultant.

The combined capacity of the top 20 reached 10.81 million 20-ft. equivalent units (TEUs) on Jan. 1, 2010, compared with 10.63 million TEUs a year ago.

The leading carriers idled capacity currently stands at 743,000 TEUs, equivalent to 6.9% of their operating fleet. This is more than double the 328,000 TEUs of idled capacity, or some 3.1% of the fleet, on Jan. 1, 2009.

There were no new entrants to Alphaliner's top 20 rankings, although as a group their share of total liner shipping capacity slipped from 81.6% to 79.2 % over the year.

Danish carrier Maersk Line retained its overall lead, followed by Geneva-based Mediterranean Shipping Co. and then France's CMA CGM.