Here's why:
* The vowel sound in "oxygen" is a long "o" sound, similar to the "o" in "go".
* Short vowel sounds are typically found in words where the vowel is followed by a single consonant, like "cat" or "dog".
* Long vowel sounds can be created in various ways, but in "oxygen" the "o" is followed by a consonant blend ("xy") which makes the vowel sound long.
So, the vowel sound in "oxygen" is actually a long vowel sound, not a short vowel sound.