Gas effects on the transport rates of ZnSe in closed systems were investigated. An ampoule (10 mm 90 mm) was fabricated from a quartz tube which had been cleaned in a hydrogen flow at about 1000°C for 5 hours. The source material was polycrystalline ZnSe of 6N purity with about a 3 to 6 mm particle size. Ar, H 2 or He gas was introduced under pressure p, along with the source. The ampoule was sealed and placed in an electric furnace for 15 hours. The source temperature was 1069°C, and the growth end temperature was 1048°C. Here, the transport rate was defined as J. J a r g o n started to decrease at p a r g o n = 9 Torr, J h y d r o g e n decreased at p h y d r o g e n = 45 Torr, and J h e l i u m was almost constant in all over the p h e l i u m range. The thermal conductivity of helium is almost 10 times that of argon gas, but similar to that of hydrogen gas. It was considered that J h y d r o g e n was intermediate between J h e l i u m and J a r g o n since hydrogen is a reactive gas. It was concluded that J a r g o n and J h y d r o g e n had a diffusion limited mass transport region.