ANCHORAGE, Alaska -- In the quest for oil-free power, a handful of small companies are staking claims on the boundless energy of the rising and ebbing sea. The technology that would draw energy from ocean tides to keep light bulbs and laptops aglow is largely untested, but several newly minted companies are reserving tracts of water from Alaska's Cook Inlet to Manhattan's East River in the belief that such sites could become profitable sources of electricity.