This thesis will study modal omega-automata, i.e. omega-automata that have besides standard transitions also may-transitions. A modal omega-automaton describes two languages: the language Low of words acceptable with standard transitions and the language High of words acceptable with all transitions. Alternative semantics is that the automaton describes each language that is a superset of Low and a subset of High. Modal omega-automata can be produced by development versions of tools Seminator and Spot. The goal of this thesis is to explore possibilities for state-space reduction of modal automata based on the concepts of automata pruning and quotienting. More precisely, the author will generalize the concepts of pruning and quotienting to modal omega-automata, define some simulations for these automata, and prove or disprove the correctness of pruning and quotienting based on these simulations. For the correct cases, the author will implement computation of the respective simulations and reductions by pruning and quotienting. The reductions will be experimentally evaluated against reductions by Spot applied to omega-automata without may-transitions and with may-transitions transformed to standard ones.