Abstract. Standard formation scenarios for Low-mass X-ray Binaries (LMXBs) require careful fine-tuning of parameters at essentially every stage of the envisaged formation processes. This makes LMXB formation an extremely low-probability event. We here discuss various constraints on the parameters of the primordial binary system for the survival of the binary through formation stages like common envelope evolution and supernova explosion. The dependence of these constraints on the parameters affecting the above processes is demonstrated. The probability of formation of possible pre-LMXBs is then calculated for a given distribution function of primordial binaries. An analytical method is suggested for the calculation of pre-LMXB distribution functions which can be used for LMXB population synthesis.