This is a comprehensive list of use for para and por that I found. Check it out. http://www.spanishnewyork.com/automatic/porpara.php
In this case, I think the oil is for the use of the lamp, so para is appropriate.
Feb 8, 2016 - In English, you only use A/AN for countable nouns. You can have AN egg, A chicken, A glass of something. You cannot use A/AN for non-countable nouns, like water, oil, milk, sand, air, sunlight.
Some will point out that you COULD say, "Do we have an oil for the lamp?", but that is really a short way of saying "Do we have a type of oil for the lamp?", which is not what the Spanish sentence says. 'Type' is countable, just like 'glass' in 'a glass of milk'.
Hope that helped. :)
September 21, 2017 - The endings on the verbs tell you if it's I, you, he/she/it, we, you (plural), or they. In this case, tenemos is the we form. There is a consistent pattern to the conjugations.
It's very important that you get this. Here is an introduction to conjugating Spanish: http://www.wikihow.com/Conjugate-Spanish-Verbs-(Present-Tense)
Here is a free very well done series of YouTube videos for beginners in Spanish to get you a better start over all: https://www.youtube.com/watch?v=gBJMt1_xjTMindex=1t=617slist=PLKcUX0UhNu4XgKYZTI-bvVIzadPn-rkUQ
SpanishDict http://www.spanishdict.com/conjugate/gustar has many features you will find useful. These conjugation charts are excelent. Hovering on the names of the various tenses (Preterite) gives you an example of that tense, and clicking on them takes you to a discussion of how that tense is used. Clicking on any of the bold words takes you to a discussion of that concept.
Using the conjugation charts in SpanishDict is very good at getting you used to the patterns and becoming familiar with the names of the tenses. Many of the commonly used verbs in Spanish are irregular - they have a pattern a bit different from most Spanish verbs. However, because you use them a lot, you get used to them quickly.