Several studies have shown that different organisms are able to produce methane (CH₄) in oxic conditions, however the contribution of oxic methane production (OMP) to CH₄ emissions from lakes versus the CH4 produced in anoxic sediment has been hotly debated. This doctoral thesis studied the net production rate (P_net) over five lakes and in different time scales. P_net rates were defined as the balance between OMP (adds CH₄) and CH₄ oxidation (removes CH₄) in the lake surface mixed layer. Using modelling approaches, it was shown that OMP could contribute up to 90% percent of the CH₄ emissions, but it depends on the lake and time period analyzed. Diurnal cycles of P_net rates and empirical correlations suggest phytoplankton could play an important role on OMP. The insights of the thesis contributed to predict of CH₄ emissions from lakes and it helps to understand the role of lakes on global methane budget.