(Solid + fluid) and (vapor + liquid) equilibria for the binary systems (propane + diamantane) and (ethane + diamantane) were determined according to the synthetic method in the temperature range 360-510 K and in the pressure ranges 0.3-14 and 0.3-200 MPa, respectively. Also, for both systems the high-temperature branch of the three-phase curve (solid diamantane + liquid + vapor) was determined. In both systems, this curve starts at the second critical endpoint where the three-phase curve intersects the vapor-liquid critical curve and runs to higher temperature with a negative slope dP/dT to the triple point of diamantane. Due to a solid-solid transition of pure diamantane, the three-phase curve (solid diamantane + liquid + vapor) of both systems shows an abrupt change in slope at the point where it intersects the solid-solid transition curve of diamantane. This quadruple point SISIILV is found for (propane + diamantane) at T = 442.64 K and P = 4.110 MPa and for (ethane + diamantane) at T = 445.49 K and P = 9.35 MPa. Some vapor-liquid critical points at low mole fractions of diamantane are reported as well. The coordinates of the second critical endpoint of the (solid diamantane + liquid + vapor) curve are T = 416.28 K and P = 22.81 MPa for (ethane + diamantane) and T = 402.46 K and P = 6.265 MPa for (propane + diamantane).