In humans, semen is usually ejaculated into the posterior vaginal fornix in direct contact with cervical mucus,[4] though sperm may swim from other areas of the vagina or vulva to the cervix. The average volume of semen produced at ejaculation is 2 to 5ml (about 1 teaspoon),[5] containing an average of 182 million sperm.[2] Only a small proportion of the sperm in each ejaculation reach the site of fertilization in the fallopian tubes, their numbers decreasing exponentially as they progress through the female reproductive tract.