It's a form of fornication. Oral sex is wrong before marriage, the same as sex. You just have to hold it in before you get married, and don't put yourself in those kinds of situations where you will be tempted to do them.
Far too often we focus on the “recreation” aspect of sex without recognizing the “re-creation” aspect. Yes, sex is pleasurable. God designed it that way, and He wants men and women to enjoy sexual activity (within the confines of marriage). However, the primary purpose of sex is not pleasure, but rather reproduction. God does not outlaw sex before marriage to rob us of pleasure, but to protect us from unwanted pregnancies and children born to parents who do not want them or are not prepared for them. Imagine how much better our world would be if God’s pattern for sex was followed: fewer sexually transmitted diseases, fewer un-wed mothers, fewer unwanted pregnancies, fewer abortions, etc. Abstinence is God’s only policy when it comes to sex before marriage. Abstinence saves lives, protects babies, gives sexual relations the proper value, and most importantly, honors God.
Oral sex and sex = same thing, just a different hole.