Gasior competed for the Polish squad in two swimming events at the 2008 Summer Olympics in Beijing. He raced to a sixth-seeded time in 1:48.52 coming to the top-eight final to dip beneath the FINA B-standard (1:48.72) by two tenths of a second (0.2) at the European Championships five months earlier in Eindhoven, Netherlands. In the 200 m freestyle, Gasior rounded out the field to eighth in the last of eight heats with a frustrating 1:49.25, trailing eventual Olympic champion Michael Phelps of the United States and runner-up Park Tae-hwan of South by nearly four seconds, and missing the semifinals with a thirty-fourth place finish from the prelims. Gasior also teamed up with Łukasz Wójt, Michał Rokicki, and Przemysław Stańczyk in the 4 × 200 m freestyle relay. Swimming the lead-off leg, Gasior recorded a split of 1:48.40, and the Polish team went on to finish heat two in seventh place and fourteenth overall with a final time of 7:18.09.