High Rayleigh number thermal convection in tilted rectangular enclosures of different aspect ratios (1,3, 6, and 10) and angles of inclination (0 degrees, 30 degrees, 60 degrees, 90 degrees, 120 degrees, and 150 degrees) is experimentally studied for 1.85 x 10(6) <= Ra <= 1.04 x 10(11) employing compressed gases. For a fixed Rayleigh number, aspect ratio is found to have a discernible effect on Nusselt number for all the cases, except for the horizontal enclosure case (0 degrees), and this decreasing effect becomes stronger as the angle of inclination increases. Nusselt number is observed to monotonously decrease as the angle of inclination is increased, for any given Rayleigh number. A new set of correlations for Nusselt number, valid for the investigated range of studied variables, is proposed. An Ra cos El scaling is also found to work reasonably well for angles of inclination less than 60 degrees. (C) 2019 Elsevier Ltd. All rights reserved.