The use of forced flow of liquid provided a means of significantly increasing the value of gas hold up due to its effect
on mixing time. Both gas and liquid flow rates contributed to the promotion of mixing in the reactor. Good correlations for the gas hold up and volumetric mass transfer coefficients are presented in the HTLB. This work covers methane flow rates and also variables like the ratio of separator volume to bioreactor volume (S), L/D, UsG and UsL for methane which, have not been considered in the previous studies. This research has been devoted to covering these variables to obtain a generally applicable equation for the HTLB design and biomass production, especially from natural gas. Bubble flow regime is the most desirable regime to achieve best transport and mixing phenomena. In bubble flow regime, high biomass production occurred at 50%(v/v) methane, as the optimum gas mixture. It was observed that the rate of oxygen transfer and methane is critical. In this study, some experimental correlations were suggested for mixing time, gas holdup and volumetric mass transfer coefficients.