Formal:
* 세상에! (Sesang-e!) - This is the most common and neutral way to express surprise or astonishment. It literally means "In the world!"
* 맙소사! (Mabso-sa!) - This is a more formal and dramatic expression, similar to "Goodness gracious!" or "Oh dear!"
Informal:
* 헐! (Heol!) - This is a very casual and popular exclamation used by young people. It's similar to "Whoa!" or "OMG!"
* 와! (Wa!) - This is another casual exclamation used to express surprise, amazement, or admiration.
* 어머나! (Eomona!) - This is a slightly more feminine expression used to express surprise or shock.
Other options:
* 아이고! (Aigo!) - This is an expression of distress, sadness, or pain. It can be used in situations similar to "Oh dear!" or "Oh no!"
* 맙니다! (Mabnida!) - This is a very formal expression of astonishment or disbelief, similar to "My goodness!" or "Good heavens!"
The best way to choose the right expression depends on your relationship with the person you are talking to, the situation, and the tone you want to convey.