In Basic D&D, Holy water is actually a much worse deal than flaming oil. I don’t know why I ever got it.Holy water does 1d8 damage to undead creatures. Not too bad: in Basic, only a fighter could reliably do more than 1d6 damage with an attack, and only if you were using the variable weapon damage optional rules. Holy water is still potentially a good choice for a rogue or a magic-user faced with undead.
Flaming oil, on the other hand, did 1d8 the first round and 1d8 the second – twice the damage. Furthermore, it hurt nearly every creature, including undead.
Not only was holy water half the damage and more situational, it also cost 25 gp per vial, compared to oil’s 2 gp.
If I were to play Basic again, I think I’d at least double holy water’s damage.