The origins of oxygen fires have been the subject of extensive study for over half a century, and test methods have been developed to define safe operating conditions and the selection of appropriate materials. The ASTM G124-18 standard test method allows analysts to compare the burning characteristics of metallic materials. Despite its numerous advantages, however, the test method has significant limitations. The test is performed in an almost static flow condition, which is often not representative of the real operating conditions of the material. Thin geometries (springs, shims) and coated material are not addressed by the standard, the typical standard sample being a rod with a diameter of 3.2 mm. The test also does not address the determination of ignition characteristics, and the energy transmitted from promoter to specimen is not precisely quantified. Considering these limitations, PIMM Laboratory (CNRS: The French National Center for Scientific Research), in collaboration with Air Liquide, has developed a complementary laser heat deposition ignition testing system. This approach allows the analyst to characterize the ignition and combustion of materials for various operating parameters (pressure up to 40 barg, gas flow velocity, initial temperature) in terms of energy and temperature ignition for rods from 0.5 to 3.0 mm. Propagation rate is characterized as well. This paper investigates how rod sample diameter and oxygen pressure affect the combustion process, with a focus on observable variables such as propagation rate and drop detachment frequency in the rod sample configuration as per the ASTM G124-18 test method; rod diameters from 1.0 to 3.2 mm and laser ignition in a gaseous oxygen (GOX) pressurized atmosphere are considered. Different materials are investigated, including pure iron, stainless steel, and a nickel-base alloy. Moreover, laser promoters associated with smart diagnostics, such as a high-speed camera and optical pyrometer, are used to determine propagation thresholds (temperature, energy) and the evolution of the burning sample temperature during the combustion process. The findings will help analysts interpret results from the ASTM G124-18 standard test method and offer inputs to oxygen fire risk assessment and design considerations for oxygen service.