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One of the methods used to fulfill application requirements in the design of finned-tube gas coolers for industrial use more adequately is to vary the spacing of the tubes. In the past there has been very little information available on the effect of tube spacing on cooler performance. This paper covers the results of a series of tests made to determine the effect of tube spacing on the pressure drop and the heat-transfer coefficient of air flowing across a bank of helically finned tubes. The tests covered a wide range of tube spacings, both at right angles to air flow and between rows in the direction of air flow. All tests were made on staggered tube rows. The tests showed that tube spacing has a marked effect on air pressure drop, but a negligible effect on the air-side heat-transfer coefficient. The number of fins per linear inch of tube had a similar effect. Baffles in the spaces at the ends of short tube rows were found to be beneficial in minimizing edge effects, the improvement in heat transfer gained by their use more than compensating for the increase in air pressure drop.