There are several alternatives. Some involve splitting the hydrogen from natural gas or an alcohol. We have a lot of natural gas and can grow the plants needed to make the alcohol.

As for electrolysis, it requires a lot of electricity. From the Department of Energy:

In 2001, the United States generated 3,779 billion kilowatthours (Kwh) of electricity, including 2,661 billion Kwh at electric utilities plus an additional 1,116 billion Kwh at nonutility producers. For utilities, coal-fired plants accounted for 60% of generation, nuclear 20%, natural gas 10%, hydroelectricity 7%, oil 3%, geothermal and "other" 0.1%. For non-utilities, natural gas plants accounted for around 32% of generation, coal 32%, nuclear 21%, "geothermal and other" (including geothermal, wind, solar, wood and waste) about 8%, oil 5%, hydroelectric at 2%, and "other gaseous fuels" (including refinery still gas and liquefied petroleum gases) 1%.



During the first 6 months of 2002, total U.S. net generation of electricity was 1,836 billion Kwh (1,235 billion Kwh from utilities and 600 billion kwh from nonutilities), about the same as for the corresponding period in 2001. Roughly half of this generation was accounted for by coal-fired power plants. This was followed by 21% from nuclear, 17% percent from natural gas, 8% from hydroelectricity, 3% from renewables, and 2% from petroleum.



So, by the DOE numbers, oil was the source for only 3% of our electricity. The question becomes where will we get the additional electricity to meet the demands for hydrogen if produced by electrolysis. Based on the DOE numbers, it seems like we won't need to import more oil to meet the demand. It'd certainly be preferable if the source were clean instead of burning more coal, but that remains to be seen.