Recent energy crises of Pakistan have triggered the interest of researchers in co-gasification. Little research work is available on Pakistani low-grade high volatile coal and biomasses derived from agricultural waste. Pakistan stands 5th in world coal reserves. Currently, only the sugar sector is fully or partially using the abundantly available sugarcane waste (baggase) as fuel for their combined heat and power (CHP) plants. Rice husk and corncob are also being utilized inefficiently by textile and rice mills to meet their energy requirements. Hence, current low level use of these resources is due to the non availability of an efficient technology. The co-utilization of coal and biomass for gasification in CFB is a new emerging technique. Accordingly, the prime objectives of this research work were to develop and operate the Circulating Fluidized Bed Gasifier (CFBG) and to investigate the influencing parameters that affect the composition of the producer gas. Accordingly, the research work was comprised of two parts; In first part, variety of coal, biomasses and coal-baggase blends (85/15, 91/9 and 94/6) were characterized physically and thermally using a thermogravimetric analyser (TGA-LECO 701). It was operated in non-isothermal mode from ambient room temperature to 950°C to characterized the coal and biomass under various operating conditions such as heating rate (40, 20 &15°C/min), feed composition and equivalence ratio (0.24, 0.30 & 0.35) and determined their impact on thermal conversion. The conversion of biomasses completed at lower temperature (750°C) than to coal and coal-baggase blends that completed at 950°C. Results revealed that biomasses had higher de-volatilization rate than to coal and coal-baggase blends due to presence of higher fraction of volatiles. Even though in sub-stoichiometric environment, increasing heat rate enhanced the conversion, however the optimum conversion was found at heating rate 20°C/min for coal- bagasse blend 91/9 and at equivalence ratio (ER) of 0.30. Further to above, heating values decreased with increasing biomass (bagasse) fraction in the blends. Arrhenius equation model was applied on TGA data to determine the kinetic parameters (activation energy and frequency factors) and observed that these variables also have very pronounced effects the kinetic parameters. The research work mainly focused to develop and operate a Circulating Fluidized Bed Gasifier (CFBG) using the result of characterization studies. Accordingly, a CFBG made of stainless steel (316) with internal diameter 81mm and total height 3900mm fitted with external gas preheater (EGH), stand pipe, cyclone and water cooled condenser was operated for temperature change 700°C to 950°C. The effect of operating parameters; temperature, ER values (0.25-0.38) and coal-bagasse blends (91/9 & 94/6) on the composition of producer gas were investigated. The temperature of the gasifier varied from 750°C to 875°C, a series of heterogeneous and homogeneous reactions took place and the gas composition obtained showed that up to the temperature 750°Cto 820°C the H2/CO molar ratio decreased from 0.82 to 0.77 but after this, H2/CO ratio began to increased and gained the values of 0.81 and 0.87 for temperatures of 850°C and 875°C respectively. Conversely, the molar ratio CO/CO2 increased from 0.57 to 0.67 with temperature variation (750°C-820°C), however a further increase in the temperature (>820°C to 875°C), decreased the CO/CO2 ratio and attained the fraction value 0.65 and 0.62 respectively. Increasing ER value not only enhanced the temperature and superficial velocity of particle but also caused to increase the fraction of CO2 and N2 in the producer gas and decrease in CO and CH4. However, increase in H2 and CO was observed at low ER value. Higher fraction of coal in feed stock, increased the molar fraction of CO2, however, the concentration of CH4 decreased due to decreasing fraction of volatile matters in blended feedstock, as biomasses contained more volatiles than to low rank coal.