What kind of oil does a Honda lawnmower use?

Honda small engines use a an engine oil 10W-30 API Grade SG (or SJ). These are older API grades that contain higher levels of zinc anti-wear additives than the current SL/SN grades, however, use of these more modern automobile oils in an emergency is acceptable as long as oil change intervals are reduced by 50%.

If Honda branded oil is unavailable, or a full synthetic oil is preferred, then use of an oil designed for a 4 stroke motorcycle in 10W-30 or 10W-40 is an option as these contain the higher levels of anti-wear additives typical of SG or SJ oils. Note that grades SH and SG are no longer licensable.