[en] Flow-induced vibration within steam generators and other heat exchanger equipment has been recognized as a significant factor in the wear and eventual failure of tubes. This paper presents data obtained by measuring the fluctuating forces induced by liquid and two-phase cross flow, on rows of tubes with pitch to diameter ratios of 1.5 and 3.0. Direct measurement of the force spectrum was possible because the tube was mounted on force transducers. The tubes within the test section were 300 mm in length and 30 mm in diameter. Results were obtained over ranges of void fraction and mass flux from 0 to 95 per cent and 375 to 4,125 kg/(m².S) respectively. A reasonably uniform spatial distribution of the void fraction was achieved through the use of a ''Koch'' type mixing unit. The reported results include the power spectral density spectra of the fluctuation forces and their corresponding force coefficients