diff --git a/slides/intro.md b/slides/intro.md
index 8b40dc50a39057f00a07cc6f957d08095429cd5c..0369ae13b489bb1ae607448ea44dd04d6b0f34ab 100644
--- a/slides/intro.md
+++ b/slides/intro.md
@@ -147,6 +147,7 @@ Preimplemented models:
 ## Flow in Porous Media
 
 <img src="img/models.png" width="650"/>
+<small><small>Credit: H. Class, R. Helmig, P. Bastian. Numerical simulation of non-isothermal multiphase multicomponent processes in porous media.: 1. An efficient solution technique</small></small>
 
 ## Darcy's law