Engine oil is typically dark-brown or black in color. At times, you might see a few drops here and there and this might be all right if you recently have had your oil and oil filter changed or performed this service yourself. This can largely be attributed to the location of the oil filter on the engine and some oil may have dripped upon some of the vehicle chassis or a small amount was spilled onto the engine when dispensing the new oil into the filler area. While a few drops shortly after an oil change might be ok, you want to make sure that "puddles" of oil do not occur.

Engine antifreeze / coolant can be either green, yellow or red depending on the type used by the vehicle manufacturer. Most vehicles have a radiator located just behind the grill. This fluid has a sweet smell to it (like maple syrup). Not enough antifreeze / coolant will cause the engine to overheat. There is usually an "overflow" or "fill" tank where you can add antifreeze / coolant to your cooling system.

If the fluid looks like clear water, than it probably is. Since most vehicles today are equipped with air conditioning, you'll likely notice drips or puddles coming from underneath the engine compartment. This is ok, since this water is condensation from the a/c system. This is the best fluid to see under your vehicle.

Brake fluid is generally clear and oily to the touch. When you depress the brake pedal, brake lines allow the brake fluid to be pushed through to each of the 4 wheels containing a "stopping device", either a brake caliper or a wheel cylinder. So any number of leaks could appear almost anywhere a weakness may exist in the system. While leakage of the brake system is rare, you'll likely feel a "soft or spongy" brake pedal feel when depressing the brakes, which can lead to brake failure if not corrected immediately.

Transmission fluid (TF) is typically red, although the color can be a "milky pink" color if it becomes contaminated. Some TF for certain vehicles may be clear or amber in color. If you have a front-wheel-drive vehicle, then your transmission is next to the side of your engine underneath the hood. If you have a rear-wheel-drive vehicle, then your transmission is located in the center of your vehicle just under the dash under that "hump" in the center. If the color of your TF appears to be brown then this would indicate that the fluid has overheated and should be changed as soon as possible.

Power steering fluid is generally red, although some vehicle manufacturers may use a fluid that is almost clear or amber. The power steering reservoir is typically mounted with the power steering pump driven by a belt on the engine. Leaks generally occur within the power steering lines.

Pink or blue fluid would indicate that your windshield washer reservoir is leaking. For the front windshield, this reservoir is under the hood in the engine compartment. For vehicles with rear wipers, it is usually mounted behind a panel in the rear left or right side of SUV's and vans.

Gasoline is a clear fluid with a strong smell and is obviously highly flammable. Gasoline is stored in the gas tank which is usually located at the rear of your vehicle. Leaks can occur if you bottom out your vehicle, causing damage to the gas tank. There are also fuel lines that run underneath the vehicle up to the engine. Leaks can also occur within the fuel line (rare), but are most likely to occur at a connection point. Gasoline leaks should be repaired immediately due to a fire hazard.

Diesel fuel looks like light oil. While not as flammable as gasoline, it can ignite in the right conditions. Leaks should be taken care of as soon as possible.

Gear oil is a light tan or black color and is considered a "heavy" or "thick" oil. Leaks can occur in your manual transmission, differential (rear-end on rear-wheel-drive vehicles) or axle. Since gear oil is used widely among certain components, a gear oil leak may be present at a number of locations underneath a vehicle. Any leaks should be repaired as soon as possible.

Battery acid is a clear fluid that contains sulfuric acid and will smell like rotten eggs. A leak would typically indicate that your battery casing is cracked and the battery should be replaced immediately. Since battery acid is corrosive, any contact with skin should be washed and flushed with water as soon as possible.

Shock and strut fluid is typically dark brown. Shocks and struts can "ooze" their fluid and this will be evident by a stain on the outside of the shock or strut housing. There is no refilling of this fluid so they must be replaced (usually in pairs or all four at the same time).