Air-cargo traffic, a leading indicator of general business activity, shrank in May from a year earlier after slowing over recent months. The data are a sign that high oil prices may be hampering world economic growth, according to the International Air Transport Association, which compiles the figures.

Roughly 40 percent of goods shipped worldwide, measured by value, move by air. That includes high-margin products such as sophisticated industrial equipment, consumer electronics, auto parts and clothing, as well as perishable items such as food.

The volume and value of air cargo rose steadily over the past few years as much of the global economy picked up and the pace of business quickened.

Cargo aircraft are an increasingly important market segment for plane makers Airbus SA and Boeing Co., which recently announced plans for a new large cargo jetliner.

But the pace of growth in air cargo has dropped significantly since February. In May, the volume of traffic fell 1.6 percent below the level of May 2004. It was the first clear drop in more than two years.

Air-cargo traffic is measured by both the weight of goods and the distance they fly.

"The obvious conclusion is that the high price of fuel is starting to affect industries beyond those that are super-exposed" to oil prices, such as airlines, said Anthony Concil, chief spokesman for the IATA, a global airline trade group in Geneva.

Companies feeling a pinch from oil prices could be curtailing production, purchases and therefore shipments. Concil said that while the IATA had expected high oil prices to slow economic activity, the recent slump has surprised IATA economists.

The May drop in air-cargo traffic came as the global volume of passenger traffic continued to rise, climbing 8.8 percent from May 2004. Airlines worldwide are reporting greater numbers of people flying, although ticket revenue isn't rising at the same pace. Sluggish revenue growth, combined with sharply higher fuel prices, is hurting the profitability of passenger airlines. The IATA predicts the global industry will show a combined loss of $6 billion this year, with much of that coming from a handful of traditional airlines in the United States.

Now, the sharp drop in cargo traffic could signal worse times ahead for passenger airlines, whose fortunes are closely correlated to broader economic growth. IATA Director General Giovanni Bisignani said in a prepared statement that airlines "can expect a downward trend as the decline in economic activity works its way through the economy."