SHORT ANSWER: Yes, it is a sin to give or receive oral sex outside of marriage. God has designed all sexual activity for the context of a monogamous, life-long marriage.
LONG ANSWER: God has a specific plan for human sexuality -- to be experienced and enjoyed in the context of a married husband and wife. This includes all forms of sexual activity, including oral sex. (However, there are some sexual activities that are explicitly taught as sin, whether married or not, such as incest, rape, or bestiality.)
There are two main terms that the Bible uses for sexual sin:
- Adultery– When a married person has sex with someone other than their spouse. For example,
- "You shall not commit adultery." (Exod. 20:14, Deut. 5:18)
- "For out of the heart come evil thoughts—murder, adultery, sexual immorality, theft, false testimony, slander" (Matt. 15:19)
- Sexual Immorality– A general term for any kind of sexual sin (but often referring to sex outside of marriage). For example,
- "We should not commit sexual immorality" (1 Cor. 10:8)
- "The acts of the flesh are obvious: sexual immorality, impurity and debauchery" (Gal. 5:19)
- Lust– A serious fixation on something that isn't ours to have. This doesn't have to be sexual in nature (such as a lust for wealth), but when it is, it usually entails wanting another person's body for our own sexual pleasure. For example,
- "But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart." (Matt. 5:28)
- "It is God’s will that you should be sanctified: that you should avoid sexual immorality; that each of you should learn to control your own body in a way that is holy and honorable, not in passionate lust like the pagans, who do not know God;" (1 Thess. 4:3–5)
So, where does oral sex fall?
The first one, adultery, is pretty clear. If you're married and you're having intercourse with anybody but your spouse, you're committing adultery.
The third one, lust, is a state of the mind and heart, not a behavior. So, oral sex doesn't explicitly fall into that category. (But you can be sure that it's involved. More on that later.)
But what about the second one? What exactly is sexual immorality? Everybody seems to agree that intercourse is sexual immorality. But what about everything else? There's a whole lot of stuff that a dating couple can do prior to going all the way. Where's the line for sexual immorality?
Here's a helpful way to answer the question: If it involves sexual body parts, then it's sexual sin. Sexual body parts include the penis, vagina, breasts, and butt. So, if you're doing anything that involves one or more of those sexual body parts, then it's sexual sin. That includes whether your clothes are on or off and whether you're the one feeling up or being felt up.
Does that mean that anything not involving sexual body parts is okay? Not necessarily. That's when you have to consider lust. Lust is an ambiguous term because it differs for every person. For some, a sexy midriff or a pair of ripped arms in a tight shirt might be enough to get the mind wanting more. For some, simply getting a shoulder massage from the opposite sex is enough to get sexually aroused.
So, you have to be aware of your own body and your heart to understand what things make you lust. Then you have to draw the line before you get to that point. Usually, that happens long before oral sex begins. So, be careful about drawing a line based simply on a behavior rather than the condition of your heart (Matt. 5:27-28).