The only way you can get a tan is from the sun, as stated above. UV rays cause the skin to react and produce more melanin, thus making your skin darker. Heat does NOTHING. If you're getting darker it's probably because you're convincing yourself your skin is darker.
http://health.howstuffworks.com/sunscreen.htm
Tanning lotions usually have an SPF that help you not fry like an egg. Tanning oils, on the other hand... well, it's kinda like rubbing your body with crisco and then exposing it to a very large heat sorce (the sun) and "cooking" your skin until it's nice and golden brown. The principle is the same.
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Sage knows our mythic history, King Arthur's and Sir Caradoc's
She answers hard acrostics, has a pretty taste for paradox
She quotes in elegiacs all the crimes of Heliogabalus
In conics she can floor peculiarities parabolous
-C'hi