To assure adequate fracture resistance of cryogenic pressure vessels designed to operate at a minimum design metal temperature (MDMT) colder than 77K, current ASME VIII-1, UHA-51 rule requires that the weld metal (WM) meet or exceed 21 mils lateral expansion (LE) at 77K as determined using Charpy V-Notch (CVN) impact test. To the credit of this rule, cryogenic pressure vessels fabricated to date meeting the WM CVN 21 mils LE requirement had continued to serve well - without any adverse incident - in numerous applications across the world, at cryogenic temperatures colder than 77K. However, a critical examination of the underlying research revealed that the technical basis used for establishing the above requirement can be further improved. The present research used an insightful data analysis approach to provide a rational basis for describing a fracture resistance parameter that also reaffirmed the WM CVN 21 mils LE at 77K toughness requirement for cryogenic service colder than 77K. While the fracture resistance parameter remains applicable to both 77K and 4K service, its use offers a tremendous benefit to the cryogenic equipment manufacturers as the fracture resistance parameter for both 77K and 4K service can be evaluated using LE, KIc and YS values measured at 77K.