This paper presents an experimental study for buoyancy-induced natural convection in the Rayleigh number range of 8.7 x 10(2)-2.0 x 10(9) inside rectangular enclosures wherein the two vertical walls were heated on the right wall and cooled on the left wall, respectively. The remaining four walls are adiabatic. Temperature data were taken for aspect ratios of 1 less-than-or-equal-to A less-than-or-equal-to 20 and Prandtl numbers of 0.7 less-than-or-equal-to Pr less-than-or-equal-to 464. To gather detailed information regarding flow and heat transfer measurements, flow visualization as well as qualitative information of thermal fields (only for 8.7 x 10(2) less-than-or-equal-to Ra less-than-or-equal-to 1.5 x 10(4)) using holographic techniques were made and analysed. Results are presented for a range of Rayleigh numbers. Prandtl numbers and for various values of the aspect ratio. Furthermore, thermal correlations as a function of Rayleigh numbers and geometrical parameters and working fluids for different flow regimes were developed, which were also qualitatively verified by existing results.