The cloud is an eco-system in which virtual machine instances are starting and terminating asynchronously on user demand or automatically when the load is rapidly increased or decreased. Although this dynamical environment allows to rent computing or storage resources cheaper rather than buying them, still it does not guarantee the stable execution during a period of time as the traditional physical environment. This is emphasised even more for workflows execution, since they consist of many

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... a and control dependencies, which cause the makespan to be instable when a workflow is being executed in different periods of time in cloud. In this paper we analyse several parameters of workflow and the cloud environment that are expected to impact the workflow execution instability and investigate the correlation between them. The cloud parameters include the number of instances and their type, as well as the correlation with the efficient or inefficient execution of workflow parallel sections. We conduct a series of experiments, repeating each experiment by 30 test cases in order to evaluate instability for different cloud and workflow parameters. The results show a neglectfully correlation between each pair of parameters, as well as the tasks and file transfers within the workflow. Oppose to the expectations, the distribution of the makespan per experiment does not always comply with the normal distribution, which is also not correlated to a particular cloud or workflow parameter.