Gas liquid mass transfer was characterized in the HTLB for various combinations of two design parameters (L/D and volume of gas–liquid separator S) as well as two operational parameters (UsG and UsL) for production of biomass from natural gas. The results presented in this work in dicated the general increase in the mass transfer and gas holdup performance of the HTLB used in this study with decrease in the value of mixing time. Experimental results show that the geometric characteristic (L/D) of the bioreactor exerts an important influence on tm, and kLa, while separator volume had no significant effect on these terms at our operational conditions. However, the effect of separator value may be considered better in other ranges. Moreover, mixing time and gas holdup in the HTLB were characterized for various gas and liquid flow rates. Presence of forced liquid flow enabled the production of different flow regime to be produced.