Oil from Kitniyos
Pure clear cloudless oils derived from Kitniyos, are not, and never were, prohibited by the Kitniyos decree.
Oil was deemed to be Kitniyos because it was a very crude product, it was clouded with observable specks of Kitniyos, as we would expect of oils extracted by crushing seeds in a mortar at home.
Even so, such oil may be placed where they may drip into our Pesach food, because the decree was not intended nor designed to include that. The decree was not structured to prohibit absolutely every situation where there may be a risk of contamination.
An analysis of the Mishneh Berurah, OCh 453 MB 11
There is no need to hang a lamp burning Kitniyos oil away from food notwithstanding the not uncommon dripping from such lamps.
The MB explains this is permitted not because the risk is insignificant but because the Kitniyos custom is not applicable to these circumstances. This is the ruling of the Rama in his Sefer Darchey Moshe.
MB continues, adding more detail from the Darchey Moshe - this is permitted equally even when the oil is extracted from sesame seeds that have been pounded in a mortar that has been used for Chamets. Although there is a risk that some Chamets crumbs might now be in that oil and by soaking will be contaminating it with Chamets taste, this is not a problem.
The MB explains that it will be Battel before Pesach begins.
The MB then deflects the question that the oil has been flavoured by the Chamets taste absorbed by the mortar, which being far larger than any specks of Chamets in the mortar, will not be Battel - by explaining that sesame oil is not sharp and will therefore not be contaminated.
What emerges is that the sesame oil is a very crude product clouded with observable specks of Kitniyos. Such oil may be placed even where there is risk that it will drip into our Pesach food because the decree was not structured to prohibit absolutely every situation where there may be a risk of contamination.
Furthermore, the entire discussion is only considered because the oil is clouded with visible specks of Kitniyos. Pure clear cloudless oils derived from Kitniyos, are not, and never were, prohibited by the Kitniyos decree.
רוצה לומר שאין צריך לדקדק לתלות הנר של שמן במקום רחוק מן השולחן משום חששא שמא ינטף על מאכל דאפילו ניטף אין לאסור דבכגון זה לא נהגו להחמיר כן מבואר בדרכי משה
ומסיים עוד שם דאפילו כתשו אותן השומשמין שעושין מהן השמן במכתשת שכותשין שם חמץ נמי לית לן בה והטעם דאפילו נתערב בו משהוא נמי בטל
בששים קודם הפסח
ואין לומר שמקבל טעם מהמכתשת של חמץ דהא צונן אין מפליט ומבליע