Well... if 98% sulfuric acid means 98% by mass, then that's 98g of H_{2}SO_{4} per 100g H_{2}O. 98g of H_{2}SO_{4} is about 1 mol, and 100g H_{2}O is about 0.1 L, which means that it's about 10M.

And for 500M you'd need 500 mols H_{2}SO_{4} per liter of water, right? Which translates to about 49.045 kg of solid H_{2}SO_{4}! Seems unrealistic to me, but at the same time I can't find the solubility of solid/anhydrous H_{2}SO_{4} anywhere.