The Mishnah (Avodah Zarah 35b, which was on this Monday's Daf in the Dafyomi cycle) states that Rebbi and his Beis Din permitted the oil of non-Jews.

Kol Tuv,

Dovid Bloom

Follow-up reply:

Here are some insights from the Gemara that we are learning at the moment in the Dafyomi cycle, concerning your question why the people of Ludkiya did not suspect the Shali'ach of mixing in non-kosher ingredients:

1) The Gemara (Avodah Zarah 38b) cites Rav Safra who said that there is no reason to prohibit cooked oil of non-Jews. What do we have to be worried about?

(a) We need not be worried that forbidden items were mixed into the oil because if one mixes in such items it merely makes the oil decay and become smelly.

Rashi (DH I'arovei) explains that the Gemara is referring to mixing in wine. The Rambam (Hilchos Ma'achalos Asuros 17:22) writes that the Gemara is referring to cooking the oil with Tereifah meat. At any rate, according to both Rashi and the Rambam we assume that if forbidden foods are mixed into the oil, this damages the oil, so we need not be concerned that the Shali'ach would do this with the oil for Ludkiya.

(b) We need not be concerned that the oil was cooked in non-kosher utensils, because the Halachah follows the opinion that Nosen Ta'am li'Fegam is permitted. If the utensils have not been used within the last 24 hours, any forbidden foodstuffs absorbed in the walls of the utensils will give a bad taste to any food cooked in them, and thus they do not make this food forbidden.

2) If there would be a financial incentive to "forge" the oil, we can prove from Rashi (beginning of Avodah Zarah 39b, DH Asurin) that this would represent a problem. Rashi writes that one may not send meat with a Nochri Shali'ach, nor the Techeles dye required for dying the strings of Tzitzis, because since these two items are expensive we suspect that the Shali'ach will forge and switch them for cheaper items.

3) The Shulchan Aruch (Yoreh Deah 114:7) rules that the oil of Nochrim is permitted. The Kaf ha'Chayim #33 adds that this is only when we know that it is pure. If there is reason to believe that forbidden items have been mixed in with it, we do not have a Heter. It all depends on up-to-date knowledge of the local circumstances.

4) It must be that in the times of the Gemara, the other ingredients that oil contained were much simpler. Nowadays, manufactured items may contain many additives, which is why many people nowadays are particular only to buy oil with a Hechsher.

Kol Tuv,

Dovid Bloom