What is the recommended oil theses days ? Synthetic or petroleum based ?
Search on "oil" here, some people buy Valvoline or Penzoil by the quart, others swear by synthetics like Mobil One 2T (recently discontinued), Amsoil Saber, Stihl Ultra, etc. Just make sure you're buying air cooled power equipment oil, not snowmobile or outboard motor oil. I used to buy Amsoil for $9 a quart, then found out my Dolmar dealer was selling 6.4oz of Dolmar synthetic for $1.33.
Good oils will carry a JASO FC rating, the best ones are FD. Figure 32:1-40:1 for Valvoline, and 40:1 or 50:1 for good synthetic. If you're using an old saw, don't use the ratio recommended when the saw was new, use the ratios I mentioned.