An oasis in a dream symbolizes a place we wish to reach or visit through our positive thoughts and habitual activities. Oasis in your dreams could manifest to be such as peace, tranquility and serenity where everything seems okay. It is also possible that it symbolizes our escape from responsibilities.
Take it in stride that seeing an oasis in a dream is very positive and could very much lead to an opportunity for your waking life where there is some peace and protection from worrying thoughts by taking the focus away from what we normally perceive as excess negativity.