U.S. sales faltered somewhat in May as the seasonally adjusted rate for the month did not meet expectations or keep up with the pace during the first four months of the year.

The industry did record its 21st consecutive year-over-year sales increase, however, so growth is continuing.

May’s SAAR was 13.7 million, down from the prior month’s 14.4 million and the 14.5 million rate through April. It was higher than year-ago’s inventory-depleted 11.7 million, and the revised year-to-date SAAR through May of 14.3 million is well above five-month 2011’s 12.7 million.

Total light-vehicle volume for the month was 1.330 million. That equals a daily selling rate of 51,161 over the month’s 26 selling days, 16% above year-ago’s 44,094 over 24 selling days.

However, the increase from May 2011 is somewhat misleading. The year-ago month was the first to be fully impacted by the inventory shortage that resulted mostly among Japan-based auto makers due to the earthquake and tsunami that decimated parts of Japan in March, causing most of the automotive industry there to shut down for several weeks.

Thus, huge year-over-year increases by Toyota (72.9%), Subaru (36.9%) and Honda (36.3%) need to be somewhat tempered.

Market leaders General Motors and Ford recorded tepid gains of 2.4% and 3.9%, respectively.

Chrysler reported another gargantuan increase in May. Its 20.1% rise was its 26th straight but the lowest since May 2011’s 18.8%.

South Korea-based Hyundai posted an increase of 4.5%, while Kia suffered a downturn of 0.9%, its first since August 2010. Although that ended a period in which Kia averaged monthly increases of 35%, the comparison with year-ago is less favorable, because both Korean auto makers likely benefited from inventory-related lost sales by the Japanese.

May 2011’s year-over-year deliveries were up 30.8% for Hyundai and 66.2% for Kia, gains neither has matched since.

Among other high-volume manufacturers, Nissan recorded an 11.3% increase and Volkswagen was up 18.5%.