Ejaculation fluid comes from several glands and organs working together, not just one source. Sperm cells make up only about 2 to 5% of the total volume. The rest is a mixture of fluids produced mainly by the seminal vesicles, the prostate gland, and a few smaller glands, all released in a specific sequence during ejaculation.
The Seminal Vesicles: The Largest Contributor
Two small glands called the seminal vesicles sit behind the bladder and produce the majority of ejaculation fluid, roughly 55 to 61% of the total volume. This fluid is thick, yellowish, and rich in a sugar called fructose, which serves as the primary energy source for sperm once they leave the body. The seminal vesicles also produce compounds that help the fluid initially clot into a gel-like consistency right after ejaculation, which may help keep sperm near the cervix.
The alkaline nature of seminal vesicle fluid is critical for sperm survival. The vaginal environment is naturally acidic, and without this buffering fluid, sperm would die quickly. Compounds like spermine and spermidine in the fluid help neutralize that acidity, keeping the pH of semen between 7.2 and 8.0.
The Prostate Gland: The Second Source
The prostate gland, a walnut-sized organ below the bladder, contributes roughly 25 to 37% of the total fluid. Prostate fluid is thinner and milky, packed with enzymes, citrate, and lipids. One of its key jobs happens after ejaculation: enzymes from the prostate gradually break down the gel formed by seminal vesicle secretions, turning semen from thick to liquid over the course of about 5 to 30 minutes. This liquefaction process frees the sperm to swim.
The prostate also produces PSA (prostate-specific antigen), the same protein measured in prostate cancer screening. In semen, PSA acts as one of the main enzymes responsible for that liquefaction process.
The Testes and Epididymis: Where Sperm Come From
The testes produce sperm cells, which then mature and are stored in a coiled tube called the epididymis that sits on top of each testicle. Together, the testes and epididymis contribute only about 5% of the total ejaculate volume. Despite being a tiny fraction of the fluid, this is the portion that contains the actual sperm cells, typically 200 to 500 million per ejaculation. The epididymal fluid also carries enzymes that help sperm gain the ability to move effectively.
Bulbourethral Glands: The Pre-Ejaculate
Two pea-sized glands called the bulbourethral glands (sometimes called Cowper’s glands) sit just below the prostate. They produce a clear, slippery mucus before ejaculation, not during it. This pre-ejaculate fluid flushes residual urine out of the urethra, neutralizing any leftover acidity so sperm aren’t damaged as they pass through. These glands, along with small urethral glands, account for about 2 to 5% of total semen volume.
How the Fluids Combine During Ejaculation
These fluids don’t all arrive at once. They’re released in a specific order, and the composition of semen actually changes from the first drops to the last. First, the bulbourethral glands release their mucus to clear the urethra. Next comes prostate fluid, followed by secretions from the seminal vesicles. The sperm-carrying fluid from the testes and epididymis is ejaculated in between. A final flush of fluid follows to clear remaining sperm from the urethra.
This sequencing means the first fraction of an ejaculate is prostate-heavy and contains most of the sperm, while the later fractions are dominated by seminal vesicle fluid. It’s one reason why the withdrawal method of contraception is unreliable: sperm are concentrated in the earliest portion released.
What Affects Volume
A normal ejaculate measures at least 1.4 milliliters, according to current World Health Organization reference values, though most men produce between 2 and 5 milliliters. Several factors influence how much fluid your body produces.
Abstinence time is the most obvious one. Longer gaps between ejaculations generally mean more stored fluid from the seminal vesicles and prostate. Hydration plays a role too, since all of these glands need adequate fluid to produce their secretions. A 2023 study looking at diet and lifestyle found that regular egg and milk consumption was associated with higher semen volume, with daily egg eaters averaging 4.0 mL compared to 3.1 mL among those who rarely ate eggs. Age also matters: the seminal vesicles and prostate gradually produce less fluid as men get older, and conditions like benign prostate enlargement or infections in the seminal vesicles can reduce volume as well.
Medications can have a significant effect. Alpha-blockers prescribed for prostate issues sometimes cause retrograde ejaculation, where fluid flows backward into the bladder instead of out through the penis. Certain antidepressants and blood pressure medications can also reduce volume.