Standard molar Gibbs energies of formation of Sr4Zr3O10(s) have been determined for the first time by measuring Sr(g) pressures over the three phase mixture {Sr4Zr3O10(s) + SrZrO3(s) + Zr1-xOx(s)} using the Knudsen effusion mass-loss technique employing a Sartorius microbalance, model 4410, and are given as : Delta(f)G(m)(Sr4Zr3O10,s,T) +/- 20(kJ.mol(-1)) = -5946.8 + 1.0070(T/K), (1157.5 less than or equal to T/K less than or equal to 1370.5). Using the molar heat capacities for Sr(s,1), Zr(s), and O-2(g) from literature and that for SrZrO3(s) from our previous work, Delta(f)H(m) degrees(Sr4Zr3O10,s, 298.15 K) has been calculated as -(5985.4 +/- 49)kJ.mol(-1). A value of Delta(f)H(m) degrees(Sr4Zr3O10, s, 298.15 K) = -(5972.8 +/- 44)kJ.mol(-1) has also been calculated using the values for the function : Phi = (Delta(degrees)(T)S(m) - Delta(298.15 K)(T)H(m)/T) for SrZrO3(s), Sr(g), Zr0.72O0.28(s), and Sr4Zr3O10(s) from literature. The value of -(5972.8 +/- 44)kJ.mol(-1)(the third-law value) is recommended for Delta(f)H(m) degrees(Sr4Zr3O10, s, 298.15 K).