diff --git a/README.md b/README.md
index ac4af28..55a5a2b 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,17 @@
 # Paralelización de simulación de permeabilidad
 
+## Paso inicial en entorno NIX
+
+Ejecutar en la carpeta del proyecto
+
+```
+nix-shell
+```
+
+y seguir todos los pasos subsiguientes en ese entorno.
+*No hace instalar python3, pip, gfortran, gcc y build-essentials pues están provistos por el nix-shell.*
+Para más info ver el archivo `shell.nix`. 
+
 ## Instalación de las librerías (Python 3)
 
 Como requisitos previos a la instalación hace falta tener:
diff --git a/requirements.txt b/requirements.txt
index 087add0..be65f92 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -59,8 +59,8 @@ packaging==23.1
 pandas==2.0.1
 pandocfilters==1.5.0
 parso==0.8.3
-petsc==3.19.0
-petsc4py==3.19.0
+petsc==3.19.4
+petsc4py==3.19.4
 pexpect==4.8.0
 pickleshare==0.7.5
 Pillow==9.5.0
diff --git a/run_simulation.sh b/run_simulation.sh
index 143c8c0..d56707e 100755
--- a/run_simulation.sh
+++ b/run_simulation.sh
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 source venv/bin/activate
 mpirun python3 mpirunner.py
diff --git a/shell.nix b/shell.nix
new file mode 100644
index 0000000..7ffa905
--- /dev/null
+++ b/shell.nix
@@ -0,0 +1,17 @@
+# nix-shell -p [ (python3Full.withPackages(ps: with ps; [ pip ])) gfortran zlib]
+
+with import <nixpkgs> {};
+
+stdenv.mkDerivation {
+  name = "python-env-petsc";
+
+  nativeBuildInputs = [ m4 removeReferencesTo ];
+  buildInputs = [ (python3Full.withPackages(ps: with ps; [ pip ])) 
+    gfortran 
+    zlib
+    gcc 
+  ];
+  dontAddPrefix=true;
+
+  env.LD_LIBRARY_PATH = zlib + "/lib:" + stdenv.cc.cc.lib + "/lib";
+}