An improved process, such as a microbiological or enzymatic process, and apparatus, such as an apparatus for producing a cellular product, comprising introducing a gaseous feed stream of at least one gas of low solubility into an aqueous medium containing a microorganism capable of converting said gaseous feed stream to a cellular product, entraining the gas in the aqueous medium, stirring the gas-entrained aqueous medium so that the gas is retained within the reactor for a time sufficient for the microorganism to convert the majority of the gas to product.