Penis size has always worried human males more than ejaculate volume - though if more men read pornography they may enlarge their ambitions.

Van de Velde suggests in "Ideal Marriage" that human semen, in one ejaculation, can be as much as 10 ml. Though G. I. M. Swyer sets his sights higher - "volumes up to 15 ml. have been recorded". Walter (again of "My Secret Life") mentions a harlot who "knew a man who spent a dessert-spoonful". It's not an area that men have tended to boast about, though in certain forms of literature a copious discharge is a definite point in the hero's favour. In pornography there is frequently talk of veritable "lakes of sperm," a state of affairs that is not all that likely to arouse ordinary folk to efforts of emulation.

Source: My Secret Life