A nickel-based alloy composition consisting, in weight percent, of: 1.0 to 3.5% aluminium, 0.0 to 3.6% titanium, 0.0 to 6.0% niobium, 0.0 to 4.9% tantalum, 0.0 to 5.4% tungsten, 0.0 to 4.0% molybdenum, 8.9 to 30.0% cobalt, 10.8 to 20.6% chromium, 0.02 to 0.35% carbon, 0.001 to 0.2% boron, between 0.001 to 0.5% zirconium, 0.0 to 5.0% rhenium, 0.0 to 8.5% ruthenium, 0.0 to 4.6 percent iridium, 0.0 to 0.5% vanadium, 0.0 to 1.0% palladium, 0.0 to 1.0% platinum, 0.0 to 0.5% silicon, 0.0 to 0.1% yttrium, 0.0 to 0.1% lanthanum, 0.0 to 0.1% cerium, 0.0 to 0.003% sulphur, 0.0 to 0.25% manganese, 0.0 to 6.0% iron, 0.0 to 0.5% copper, 0.0 to 0.5% hafnium, the balance being nickel and incidental impurities, wherein the following equations are satisfied in which W Nb , W Ta , W Ti , W Mo , W Al , W Re and W Ru are the weight percent of niobium, tantalum, titanium, molybdenum, aluminium, rhenium and ruthenium in the alloy respectively 4.2 ≤ W W + 0.92 W Re + 1.58 W Ru + W Mo and 3.0 ≤ W Al + 0.5 W Ti + 1.5 0.3 W Nb + 0.15 W Ta