I believe they just have one account type.
Trading on the FXTrade platform is performed in units, not lots. Thus, OANDA does not differentiate between standard, mini or micro accounts.
One unit is equal to one of the base currency in a currency pair. For example, one unit of USD/CHF is equal to one dollar and one unit of EUR/USD is equal to one Euro.
However, the MT4 platform does limit trade sizes in terms of lots:
1 lot = One standard lot = 100,000 units
0.1 = A mini lot = 10,000 units
0.01 = A micro lot = 1000 units
There are no minimum deposit required to trade with OANDA.
Spreads are variable and will widen during periods of volatility (such as news announcements) and during periods of low liquidity (such as off market hours).
You can review there spreads history at: https://fxtrade.oanda.com/why/spreads/recent
Hope this helps