What does the Bible say about oral sex?

Oral sex, also known as "cunnilingus" when performed on females and
"fellatio" when performed on males, is not mentioned in the Bible.
There are two primary questions that are asked in regards to oral sex:
(1) "is oral sex a sin if done before marriage?" and (2) "is oral sex
a sin if done within a marriage?" While the Bible does not
specifically address either question, there are definitely biblical
principles that apply.

Is oral sex a sin if done before or outside of marriage?
This question is becoming increasingly common as young people are told
that "oral sex is not really sex," and as oral sex is promoted as a
safer (no risk of pregnancy, less risk of sexually transmitted
diseases*) alternative to sexual intercourse. What does the Bible say?
Ephesians 5:3 declares, "But among you there must not be even a hint
of sexual immorality, or of any kind of impurity...because these are
improper for God's holy people." The biblical definition of
"immorality" is "any form of sexual contact outside of marriage" (1
Corinthians 7:2). According to Hebrews 13:4, only the "marriage bed"
is pure and undefiled. According to the Bible, sex is to be reserved
for marriage. Period. So, yes, oral sex is a sin if done before or
outside of marriage.

Is oral sex a sin if done within a marriage?
Many, perhaps most, Christian married couples have had this question.
What makes it difficult is the fact that the Bible nowhere says what
is allowed or disallowed sexually between a husband and wife, other
than, of course, any sexual activity that involves another person
(swapping, threesomes, etc.) or that involves lusting after another
person (pornography). Outside of these two restrictions, the principle
of "mutual consent" would seem to apply (1 Corinthians 7:5). While
this text specifically deals with abstaining from sex/frequency of
sex, "mutual consent" is a good concept to apply universally in
regards to sex within marriage. Whatever is done, it should be fully
agreed on between the husband and his wife. Neither spouse should be
forced or coerced into doing something he/she is not completely
comfortable with. If oral sex is done within the confines of marriage
and in the spirit of mutual consent, there is not a biblical case for
declaring it to be a sin.

In summary, oral sex before marriage is absolutely a sin. It is
immoral. It is in no sense a biblically acceptable alternative to
sexual intercourse for unmarried couples. Within the confines of
marriage, oral sex is free from sin as long as there is mutual
consent.

*While oral sex is safer than sexual intercourse in regards to
sexually transmitted diseases, it is definitely not safe. Chlamydia,
gonorrhea, herpes, HIV/AIDS, and other STDs can be transmitted through
oral sex.