As semiconductor manufacturing has entered into the nanoscale era, Bias Temperature Instability (BTI) became a major threat to reliability of CMOS circuits. This threat may even be more severe in the presence of parameter variations such as temperature and process. This paper presents simulation based analysis of BTI and parameter variations in logic gates. Delay, static and dynamic power consumptions are the metrics considered in the analysis. The simulation results show that while considering BTI only, the impact on delay is strongly temperature and duty cycle dependent. For example, in a NOR gate the delay at 75°C and 50% duty cycle is 56% higher than at 25°C; and at 40% duty cycle is 67% higher than at 60%. The results also show that BTI reduced the static and dynamic power. The analysis is redone for BTI by incorporating parameter variation. Monte Carlo simulation results reveal that BTI impact is exacerbated in the presence of parameter variations with up to 15%.