Prepare the chicken stock in a medium to large sized pot, and then bring to a boil. Add the lime leaves and lemongrass stalks to the pot, and reduce the heat to simmering. Cook for 5 minutes.

 

Remove the lemongrass, and turn the heat to high. Add the shrimp, mushrooms, chili oil, and the Thai chilies. Boil until the shrimp are done (about 2 minutes). Remove from heat.

 

Add the fish sauce and lime juice, and stir.