1. Initialize a list of n chemical species and their initial numbers of molecules X1, X2,.....Xn.

2. Initialize a list of m chemical reactions and their associated stochastic rate constants k1, k2,....km.

3. Initialize the current time t ? 0.

4. Calculate the propensity, a1, a2,...am, for each of the m chemical reactions.

5. For each reaction i , generate a putative time ti, according to an exponential distribution with parameter ai.

6. Let µ be the reaction whose putative time, tµ is least.

7. Change the number of molecules X1, X2,...Xn, to reflect the execution of reaction µ.

8. Set t ? t + tµ .

9. Go to Step 4.